Why do we "scotch" a rumour?

According to Etymonline, scotch means: "stamp out, crush," 1825, earlier "make harmless for a time" (1798; a sense that derives from the reading of "Macbeth" III.ii.13), from scocchen "to cut, score, gash" (early 15c.), perhaps from Anglo-Fr. escocher, O.Fr. cocher "to notch, nick," from coche "a notch, groove," perhaps from L. coccum "berry of the scarlet oak," which appears notched, from Gk. kokkos. Related: Scotched; scotching.

As for your question, I found only one reference to this verb used with the noun plan in OAED: Plans for a merger have been scotched.

Searching the corpora at Brigham Young University for "[scotch].[v*]" shows that it is a British expression (most occurrences were in the British National Corpus) and that although rumour is by far the most common collocate, it's also possible to scotch myths, plans, speculations, suggestions and ideas.

scotch originally also meant to scratch/score or cut.

Butterscotch is (apparently) called that because the butter mixture was cut with a knife before it set.

I can uncover no evidence to support the allegation that this is somehow a ‘British’ English use of the word. I think it’s simply English.

The OED’s sense 2 of scotch v.¹ is:

• ⁠2. trans.

  a. To render (something dangerous or undesirable) temporarily harmless or less harmful, without destroying it completely. Originally and freq. in the snake is scotched, but not killed and variants (see note). After Theobald's reading of Macbeth III. ii. 13 (see quot. 1726).

  The word was previously rendered scorch’d, as it appears in the First Folio; subsequent (esp. 19th-cent.) editions of Shakespeare often use scotch’d, though modern scholars usually prefer scorc’d. Cf. scorch v.³

  • 1726 L. Theobald Shakespeare Restored App. 186 If I am not deceiv'd therefore, our Poet certainly wrote thus; We have scotch'd the Snake, not kill'd it. She'll close, and be her self.
  • 1759 S. Fielding Hist. Countess of Dellwyn II. iv. ii. 158 The Snake was scotched, but not killed.
  • 1798 Cooke in Ld. Auckland's Corr. (1862) III. 393, I fear relaxation and too much clemency; but the snake must be killed not scotched.
  • 1820 Byron Marino Faliero III. ii. 268 Would that the hour were come! We will not scotch, But kill.
  • 1843 G. W. Le Fevre Life Trav. Physician II. ii. viii. 279 The malaria is scotched, not killed, and the intermittent returns at some future period.
  • 1879 C. Merivale Four Lect. Early Church Hist. ii. 86 It was by Augustine most of all that the Arian heresy was scotched, if not actually killed.
  • 1913 H. A. Jones Found. National Drama xiii. 214 The [Oxford] movement was thought to be killed. But it was only scotched, and it is the one operative force in the English Church to-day.
  • 1941 ‘N. Blake’ Case of Abominable Snowman xxii. 250 That wasn't enough for Andrew. He wanted the snake killed, not scotched. It was partly his personal hatred for the man.
  • 1996 Cycle Touring & Campaigning Apr.–May 25/4 So far, the snake has been scotched, not killed.

• b. To crush, stamp out (something dangerous or undesirable).

  • 1825 Q. Rev. 32 277 If we, in our own language, were to scotch the insidious forgetfulness, we might, perhaps, be accused of ‘coarse and insulting abuse’.
  • 1880 A. H. Huth Life Buckle I. iii. 189 Attempting to scotch the pestiferous germs of heresy.
  • 1908 Expositor Dec. 527 Fanaticism which constitutes a danger to mankind should be scotched.
  • 1978 T. Garvey Bones of Contention ii. 24 A political police force charged with scotching seditious activities was a long-established feature of the Russian state.
  • 1999 P. Gregory Virgin Earth 543 More particular were the thanks of the Quakers who came under his protection while he scotched the last of the royalist rebellions.

• c. To put an end to, bring to nothing, quash; to refute conclusively (a rumour, report, etc.); to frustrate (a plan or hope).

  Perh. influenced by scotch v.² 3c.

  • 1888 J. B. Mackie Life & Work D. McLaren II. xviii. 97 Mr. McLaren delivered a speech which ‘scotched’ the measure with facts and arguments.
  • 1898 Dublin Rev. Oct. 450 The Catholic Truth Society has much work to do in tracing out and scotching these lies.
  • 1926 in H. W. Fowler Dict. Mod. Eng. Usage 518/2 We hope the proposal for a Government news service for the Colonies is finally scotched by the debate.
  • 1966 Listener 2 June 792/2 The closing words of his book firmly scotch any hope we may have of evading the central question.
  • 1976 Australian 30 June 1/7 The Prime Minister‥is to meet the Russian Ambassador‥next month to scotch reports of a serious rift in Soviet–Australian relations.
  • 2008 N. Roberts Tribute xiv. 201 They wanted to have a welcome-back party‥. I scotched that.

The citation for which is:

scotch, v.1
Third edition, June 2011; online version December 2011. http://www.oed.com/view/Entry/173106; accessed 29 February 2012. An entry for this word was first included in New English Dictionary, 1910

The noun 'Scotch' is used in railway parlance as the chock which is placed on a rail to stop a 'parked up' coach or other wagon/ stock from rolling away if the brake fails/ is mistakenly released.

I imagine it got its name from the verb 'to scotch' as in to stop something in its tracks.

The term 'to scotch a rumour' was relatively common in the UK some years ago but is not heard much nowadays.

Samuel Johnson, A Dictionary of the English Language (1755) lists scotch as a verb and as a noun, and cites two instances of their use in Shakespeare—neither of them the famous one from Macbeth:

To SCOTCH. v. a. To cut with shallow incisions. [Example:] He was too hard for him directly: before Corioli, he scotcht and notcht him like a carbinado. Shakesp. Coriolanus.

SCOTCH. n. s. {from the verb.} A slight cut; a shallow incision. [Examples:] We'll beat 'em into bench holes: I have yet room for six scotches more. Shakesp. Ant[ony] and Cleopatra. Give him four scotches with a knife, and then put into his belly and these scotches sweet herbs. Walton's Angler.

Early instances of 'scotch' in the sense of 'score' or 'cut shallowly'

Early English Books Online finds several instances of scotch in this sense that are older than the ones in Shakespeare.

From William Barlow, A Dyaloge Describing the Originall Grou[n]d of these Lutheran Faccyons, and Many of Theyr Abusys (1531):

But now vnto the tother syde, these that rōne away from thē vnto these Lutherans / they go I say dysguysed strangely frō that theye were before, in gay •agged cotes, and cut and scotched hosen, very syghtely forsothe, but yet not very semely for such folk as they were and shulde be.

From John Ponet, "A Shorte Treatise of Politike Power and of the True Obedience Which Subiectes Owe to Kynges and Other Ciuile Gouernours, with an Exhortacion to All True Naturall Englishe Men" (1556):

It was dryven in to the head of temperour C. Caligula, that he was subiecte to no power, that he was aboue all lawes, and that he might laufully doo what him lusted. This lesson was so swete to the fleshe, that it was no soner moued than desired, no soner taught than learned, no soner hearde than practiced. First by like that thempire should not goo out of his owne race, he coupleth not with one, but with all his susters, like bitche and dogge. He killeth his brother Tiberius, and all his chiefest frendes: he murdereth many of the Senatours of Rome. He delited to haue honest men to be garshed, scotched and cut in the faces, and so to make him pleasure, to haue them cast to rauenous beastes to be torne and deuoured in his sight, or to be sawed asondre in the middes.

From a 1567 translation of Ovid by George Turberville:

For from these shoulders first / should fall my scotched skull: / Ere thee out of my griping handes / a mortall wight shoulde pull.

From John Foxe, Actes and Monuments of Matters Most Speciall and Memorable, Happenyng in the Church (1583):

This man [Ordinis Ducalis] beholding the meruailous constancie of the Martyrs, thirsted with the desire of Martyrdome, for that he had priuily learned the Christian religion. Therfore he not abiding for other accusers, detected himself, and worthely professed that he was a christian, openly execrating the madnesse and vanitie of the wicked Ethnikes. He therefore being caried away, was tyed vp, beyng first most bitterly beaten. After that he was parched with fire, beyng put vnto his bowels, and thē basted with salt and vinagre, and lastly, so scotched & bemangled with the shardes of sharpe and cutting shels, that his whole body semed to be all one continual wound, howbeit, by gods great goodnes afterward, it was restored to the first integritie. After this he was caried away to Sebastia, where, wt his companion Orest he was burned.

...

What great matter is it for thee I pray thee, to escape al this? If thou wilt but take & put with thy fingers a little salt & incense into the censers, thou shalt be deliuered from al these punishmēts. To this Eulalia made no aunswere, but being in a great furye shee spitteth in the tirauntes face, she throweth downe the Idoles, and spurneth abroad with her feete the heape of incense prepared to the censers: then without further delay, the hangmen with both their strengthes tooke her, & puld one ioynte from an other, and with the talantes of wilde beastes, scotched her sides to the hard bodes: she all this while singing and praysing God in this wise.

From George Turberville (again), Tragicall Tales Translated by Turberuile in Time of His Troubles out of Sundrie Italians (1587):

With sharpe and cruell sword in hand, / As one without remorse: / He seard me one, and scotcht an other, / And mangled euery corse.

And from Thomas Nashe, "Haue with You to Saffron-Walden" (1596):

Dick, no more at this time, but Nos-da diu catawhy, and all the recompence I can make thee for being like a Chancery Declaration so tiring troublesome vnto thee, is this, if thou wilt haue the Doctour for an Anatomie, thou shalt; doo but speake the word, and I am the man will deliuer him to thee to be scotcht and carbonadoed: but in anie case speake quickly, for heere he lies at the last gaspe of surrendring all his credit and reputation.

Also, after Shakespeare, from a 1611 translation of Guillaume Du Bartas, Du Brtas His Deuine Weekes and Workes Translated:

For, as a little end of burning wax, / By th' emptiness, or if it self attracts / In Cupping-glasses, through the scotched skin / Behind the Poule, superfluous humors thin, / Which fuming from the brain did thence descend / Vpon the sight, and much the same offend: ...

From a 1628 translation of Ovid's Metamorphosis:

The frighted horses, plunging seuerall wayes, / Breake all their tire: to whom the bit obayes; / The reignes, torne beame, crackt spokes, disperst abroad, / Scotcht Heauen was with the Chariots ruines strow'd.

From a 1631 translation of Fernando de Rojas, The Spanish Bawd, Represented in Celestina: or, The Tragicke-Comedy of Calisto and Melibea:

Lucrecia. She changed? Hi, hi, hi! the diuell she is: shee was faire when she met with him (sauing your reuerence) that scotcht her ouer the nose.

...

Areusa. ... What a diuell is there good in him? his hayre is cu•led, and shagg'd like a water Spaniell; his face scotcht, and notcht; he hath beene twice whipt vp and downe the Towne; hee is lame on his sword-arme, and hath some thirty whores in the common Stewes.

All of these instances seem to involve scotch in the sense of "cut shallowly (or in some cases fairly deeply)".

Early instances of 'scotch' in the sense of 'scorch'

Other early instances of scotch seem to convey other meanings.

From John Wilbye, "The Second Set of Madrigales to 3. 4. 5. and 6. Parts Apt Both for Voyals and Voyces" (1609):

A Silly Siluan, kissing heauen-borne fire, scotched his lips for his so fond desire: I not so fond, ij. but gaz'd whilst such fire burned; straight into flames, ij. was turned, And all my hart straight into flames was turned ij. And all my hart straight into flames was tur- ned, ij. was turn'd, straight into flames was turned.

From John Wells, A Prospect of Eternity or Mans Everlasting Condition Opened and Applyed (1655):

Serious and frequent thoughts of eternity, would be cordials and counsellours in all our troubles. This would sweeten and take off the bitterest potion of affliction and calamity, there is an eternity to come. Those flames I am now scotcht by, shortly death will turn into a smoak, and then I shall sail upon the pleasant sea of a glorious eternity.

From Jean-Nicolas de Parival, The History of This Iron Age (1656):

Now, in regard that this War'v as derived, like a contagion, from that of Germany, by which, as by a great fire, all the circumjacent parts were so scotched, that they kindled with the first winde: we will returne again to the Source.

These instances of scotcht seem to mean—and may indeed be typographical errors for—scorched.

Early instances of 'scotch' in the sense of "balk', 'halt', or 'chock [a wheel]'

More intriguing are the following instances, first from John Carter, A Plaine and Compendious Exposition of Christs Sermon in the Mount (1627):

The third instance toucheth men in their libertie; a thing no lesse deare to them, then their liues and liuings: to bee compelled by imprest from authority to go a mile, a league, or more at the officers pleasure, as Simon of Cyrene was, by prest, compelled to beare Christs crosse after him. In which he will haue vs value our humilitie, loyaltie, and pliablenesse to the higher powers (though forrainers, and aliens from the common-wealth of Israel, as the Romanes were) at so high a rate, as to scotch at no hardship, to giue them, or their assignes, iust content.

From Robert Norton, The Gunner Shewing the Whole Practise of Artillerie: With All the Appurtenances Therevnto Belonging (1628):

Lastly, foure or more men turning the Capstane about, with the Barres thereof, shall first make the Peece to mount vp vnto the first Pulley or Block at A, where it must be first scotched, vntill the Blocke be taken away, by taking out the Pinne or Axis of the she euer, and then the Peece is to be tauersed towards the second Block or Pully B, and so to the third C, and then to the desired place neere D. ... And after each Pully, hath performed his office, let a man be ready there with greace, vineger or Lye, to annoyot the end of the Axtree, that it may soke into the Naue, least the waight of the Peece in that Motion fire, and also to haue an eye to each of the Pullyes, that the Cable breake not. And if any danger of its breaking be perceiued, then to giue warning to them aboue to stay, and to them alow to scotch, vntill the Cable be changed or amended.

From Thomas Hill, "The Trade of Truth Advanced. In a Sermon Preached to the Honourable House of Commons, at Their Solemne fast, Iuly 27. 1642" (1642):

Men compact of meere incongruities, solaecising in opinion, speeches, actions, and whole life, yea unreasonable men, For all men have not Faith, ver. 2. Religion is the highest Reason, nothing more irrationall then irreligion. From such spirits arose those conspiracies against the Apostle, endevouring to scotch the Charriot-wheeles of Truth, when they began first to move.

From John Smith, "A Short Discourse on Atheism," in Select Discourses (1660):

For which purpose I shall need onely to touch upon Epicurus his master-notion by which he undertakes to salve all difficulties that might hold our thoughts in suspence about a [word in non-Latin alphabet], or a Creator, which is that Plenum (which is all one with Corpus) and Inane, that this Body (which in his Philosophy is nothing else but an Infinity of Insensible Atomes moving to and fro in an Empty Space) is, together with that Space in which it is, sufficient to beget all those Phaenomena which we see in Nature. Which however it might be true, Motion being once granted, yet herein Tully hath well scotcht the wheel of this over-hasty Philosophy, Lib. 1. de Finibus, Cùm in Rerum natura duo sint quaerenda, unum, quae Materia sit ex qua quaeque res efficiatur; alterum, quae Vis sit quae quidque efficiat: de Materia disseruerunt Epicurei; Vim & causam efficiendi reliquerunt. Which is as much as if some conceited piece of Sophistry should go about to prove that an Automaton had no dependency upon the skill of an Artificer, by descanting upon the several parts of it, without taking notice in the mean-while of some external Weight or Spring that moves it: or, to use his own Similitude, as if one that undertakes to Analyse any Learned Book, should tell us how so many Letters meeting together in several Combinations, should beget all that sense that is conteined therein, without minding that Wit that cast them all into their several Ranks.

From James Harrington, A Holy Oyl; and, a Sweet Perfume Taken out of the Sanctuary of the Most Sacred Scriptures (1669):

My Flesh full-oft, in which my sinful Will, / As Charrioteer, hath drove me down the Hill, / Of Worldly Pleasures; on swift moving Wheels, / Of raging Passions; (Steeds, whose Mouth neer feeles, / Religious Bit;) Pride, Lust; This Chariot mov'd, / With feerless speed; Till Grace, in thy Belov'd, / Caus'd thee, as oft, to scotch it, on / Some Stone; some blest affliction: / By which, thrown out, cast down, upon the Ground; / Thy Childe hath lain, as in a spiritual swound: / From which thou still hast raised me, by the Arme, / Of Mercy, and Me sav'd from lustful harme.

And from Samuel Blackerby, Sermons Preached on Several Occasions (1674):

And indeed, Divine Providence is never idle, but always at work, in bringing forth that which is conceived in the Divine Mind, and nothing shall hinder. I will work (saith God Esay 43.13.) and who shall let? The question implies a negation, q. d. None shall let. No 'tis not in the power of earth or hell, to scotch this Divine Wheel in its motion; As God wants no wisdom to contrive; so he wants no power to execute; and therefore may well be resolute herein, and say as you have it, Esay 46.10. I will do all my pleasure.

...

For as the word of God gives a being; so it upholds in being; thou holdest our soul in life, saith David, Psal. 66.9. The four wheels are upheld by this one wheel, or else they would soon turn into their first nothing, annihilatio est substructio influxus divini, Let God hide his face, and then the wheels are scotched, but let him withdraw his supporting influence, and then wheels are no wheels.

...

Sometimes God cures the failing of the Will, by removing those impediments, that stopt its motion. You know, if a wheel be scotcht, there is no stirring of it, until that be removed; even thus 'tis here. Sometimes the Will of man (which is the wheel of Motion) is scotcht, so that it cannot move forward, until that be removed: Hence that of the Psalmist, I will run the way of thy commandments, when thou shalt enlarge my heart, Psal. 119.32. ... My Heart was scotcht, but thou hast set me at liberty. I was pesterd with such a temptation, and with such a pressure of grief and horrour, or with such a passion and lust: but thou hast removed it, and set me at liberty.

And from Samuel Speed, "A Panegyrick to the Right Reverend, and Most Nobly Descended Prelate, Henry by Divine Providence, Lord Bishop of London" in Prison-Pietie, or, Meditations Divine and Moral Digested into Poetical Heads, on Mixt and Various Subjects (1677):

For take an upstart Groom, who setcht his rise / But lately from a Dung hill, in a trice / He huffs, and Hamans it a[t] such a rate, / As if the slip'ry wheels of Rowling Fate / Were scotcht in him, forgetting that the Son / May end as basely as the Sire begun.

In all of these instances, the sense of scotch seems to be "halt, balk, or temporarily immobilize," as a chock may prevent a wheel from rolling.

The term appears in this sense during the nineteenth century, as well. From "The Provinces," in The Spectator (July 31, 1852):

He had been told by Grant the night watchman, and Parker, the pointsman, that the train was to proceed down the east Lancashire siding, "which is a main line" ; but he found that he was on the arrival line of the Burnley station. He immediately put on his break and scotched the fore-wheels, and looked round for another break ; but finding a collision imminent, he jumped down. ...

Richard Ashton, guard of the York excursion-train which was waiting at the station, went to assist when he saw the Goole train approaching. He thought they were going too quick for a heavy train. The wheels were scotched, but he tried to oppose a further obstacle by thrusting a piece of timber through one of the wheels.

And from Elizabeth McCord (pauper) appellant and Charles Cammell and Company, Limited respondents (December 9, 1895) in The Law Reports: House of Lords, and Judicial Committee of the Privy Council (1896):

An engine-driver, employed with his fireman in the discharge of loaded wagons on a railway, took a locomotive engine and several wagons to a point on an incline, and there proceeded with the engine and one of the wagons to the place of discharge, intending to return for the other wagons in due course. The fireman uncoupled the remaining wagons and scotched them to prevent their running down the incline. One of the wagons broke away, rand down the incline, and killed a workman in the service of the same employers.

Conclusions

Instances of scotching rumors go back at least to 1902, as we see in this example from Ernest Capey, Erasmus (1902/1905):

Froude regards the story [of Erasmus's parentage] as a legend elaborated and circulated by the monks, who, lending an eager ear to the whispers of scandal-mongers, were ready to fight their opponent with any weapon that served. "It is perhaps a lie altogether; perhaps only partly a lie." We fear there is little evidence in support of the former peradventure. Erasmus never attempted to scotch the ugly rumour, on the contrary he admitted its substantial correctness.

But instances where scotched seems aligned with the sense of "halted like (figuratively) chocked wheels" go back farther. For example, from a May 1, 1895, speech by Frederick Milner on the Corrupt Practices Prevention Bill in The Parliamentary Debates [of Great Britain] (1895):

He also hoped it would be possible to strengthen the Bill in other ways and he would suggest that a clause should be added making it illegal to issue any poster or handbills of any sort or kind, except notices of meetings, addresses of candidates, and solicitations to vote. In wishing to prohibit posters and handbills, he had no wish to interfere with the circulation of pamphlets containing purely political literature. They could be excepted, but posters and handbills ought to be absolutely prohibited. He would like to call attention to the class of poster that would in no way be affected by this Bill, but would be completely scotched by his suggestion. During the late Election for Colchester the whole town was placarded with enormous yellow posters, and handbills were left at the house of every elector. ...

The expression "scotched, not killed" was quite popular through much of the nineteenth century and into the early twentieth century on the strength of the quotation from Macbeth. But it seems to me that it is at least as plausible that the "scotch a rumor" sense of scotch emerged from the idea of halting the progress of a highly mobile object by chocking ("scotching") its wheels as that it comes from the milder (or les effective) alternative to killing something.

The 1971 full-length OED traces the verb scotch in the sense of "To block or wedge (a wheel log, gate, etc.) so as to keep from moving or slipping" to 1642; and it traces the figurative sense ("To render inoperative, cripple the action of; frustrate" derived from this literal sense to 1876, with the following citation:

1876 L. Stephen Eng Th. 18th C. I. 33 The name of Spinozism was of course dreaded by them {sc. the Deists}; they take care both to avoid the imputation, and to make it undeserved by carefully scotching their logic.

A fuller version of the quoted language from Leslie Stephens, History of English Thought in the Eighteenth Century (1876) clarifies the chocking aspect of the figurative usage:

Here it is enough to remark that the whole essence of the deist position may be found in Spinoza's 'Tractatus Theologico-Politicus.' A few of the philosopher's pages have been expanded into volumes and libraries of discussion, but the germs of the whole discussion are present. Fe of the deists, it is probable, read his works; the name of Spinozism was of course dreaded by them; they take care both to avoid the imputation, and to make it undeserved by carefully scotching their logic. The immutable chain of causation recognised by Spinoza is summarily broken off by the dogmatic assertion of Free-will, which became a mark of the whole deist and semi-deist school. The legitimate descent of their theories is not the less manifest.

That is the logical path of deist principles (according to Stephen) would take it to the same conclusions that Spinoza reached a century earlier, but the deists arrested this natural progression by using the assertion of free will to prevent further that from happening.

The timing of this figurative usage of scotch underscores its availability as a source for "scotch a rumor" when that phrase emerged two or three decades later. In my view, rumors are imminently qualified to be understood as things that move and spread and whose progress may well be opposed through halting or chocking rather than through crushing or stamping out.

The 1971 OED doesn't assign "scotch a rumor" to either category—but tchrist's answer indicates that the current OED is inclined to attribute this sense of scotch to the "render temporarily less harmful without destroying" sense of the word rather than to the "render temporarily immobile" sense of the word. Either way, the wording of the OED's (relatively new) definition "refute conclusively" takes scotch a long stride closer to permanence—either as "destroy completely" or "permanently immobilize"—than one might have expected from either potential source sense of scotch.