Where does the word “snogging” come from?

Paul Beale, ed., Partridge's Concise Dictionary of Slang and Unconventional English (1989) offers this entry for the verb snog:

snog, v. 'To make love with repletion of kissing and cuddling; hence, snogging session, making love' (L.A. 1977); very common throughout WW2 [and still, 1983, not ob.: P.B.] I surmise a dial. alteration of snug, cosy, notably as in that snuggling-up which so often preludes a warmer conjunction. —2. Hence, to flirt, or to court, esp in be or come or go snogging: beatniks', adopted, ca. 1959 , ex gen s. (Anderson) The term, esp as be or go snogging, seems to have orig in the RAF, late 1930s (Partridge 1945).

However, Eric Partridge, A Dictionary of Slang and Unconventional English, Fifth Edition (1961) suggests a slightly different etymology:

snogging, be or go. To be or go courting a girl; to be or go love-making: RAF: since ca. 1937. Partridge 1945, 'Snog is perhaps a blend of snug and cod (to flatter or kid a person).'

That same source notes that "snogged up"—supposedly an RAF term dating to circa 1939—means "Smartened up, 'all dressed up.'"

The OED defines snog as follows:

snog, v (snogs, snogging, snogged): kiss and cuddle amorously the pair were snogging on the sofa; [with object]: he snogged my girl at a party

snog, n: a long kiss or a period of amorous kissing and cuddling: he gave her a proper snog, not just a peck

Origin: 1940s: of unknown origin

Which isn't terribly helpful and is already given in the question.

The word does seem to have been around for quite a while. There are a few amusing definitions:

snog, n: a stick used for 'cock-squoyling'

A glossary of Berkshire words and phrases, Volume 20, Issue 3 - Job Lowsley (1888). Sadly not helpful in this case. (For those that are interested, cock-squoyling is a game that involves throwing sticks (or squoils, snogs) at cocks).

snog (Mx.): a nod: The cow gave a snog, ie. a push with the head

A vocabulary of the Anglo-Manx dialect - Sophia Morrison, Edmund Goodwin (1924). Not much better.

Less academic sources (Punch Magazine, 1929) give definitions such as "a kind of boy", "a towel" or "a kind of bun", none of which seem to help us either.

Several sources suggest that snog is related to snug, possibly by a back-formation of snogging. In the absence of a better answer (that I can find), this would seem to be the most plausible. The OED has snuggle dating back to the 17th century, and a couple of sources (which I have lost the links for, unfortunately) suggest snog as a Scottish Gaelic word with the same pronunciation as snug.

Beneath an article reporting on an air pact with Ceylon (The Argus, Melbourne, 14 January 1950), a short column-filler adds to the mystery of the meaning of 'snog', and perhaps lifts a corner of the veil concealing the word's origins:

"Snog" popular

A Sinhalese woman ' recently returned gave a great tourist boost by saying Australia was extremely cheap and Australians very fond of "snog."

I telephoned the "Ceylon Times" to discover the meaning of snog, and a reporter explained that snogging means cheek-to-cheek dancing or "petting to music."

Very little can be concluded from this--only that a Ceylon Times reporter in early 1950 either knew the meaning of 'snog' or was willing to have the Aussie reporter on about it. And that conclusion comes with the proviso that the Aussie reporter did not make the whole thing up. The column-filler does suggest, for those willing to make great leaps from small promontories of evidence, that the term was in use, perhaps with a variety of meanings, in 1940s Ceylon.

To construct a rickety catwalk over the abyss containing the origins of 'snogging' (from which height we can perhaps at least overlook those origins), this dialectal sense, and these dialectal uses, of 'snug' suggest a possible connection, particularly considering that 'snog' is one dialectal spelling of 'snug':

(From The English dialect dictionary, being the complete ... v.5. Wright, Joseph, 1905.)

Those uses, and the sense thus attested, were collected from 1800s Cumberlands and Suffolk English dialects, where "Cum.³" references Wright's authority from

and "Suf. (C.L.F.)" Wright's authority from a correspondent,

The dialectal uses of 'snug' in the sense of 'nestling together; hugging, fondling' are not exclusive of, but rather complementary with, the Ceylon origin and sense of 'snog' relayed via The Argus, due to the long-standing and pervasive British influence on Indian English.

Note that, for the verbal sense of 'snug' attested in the Cumberland and Suffolk dialects by Wright (that is, by his referenced authority and correspondent) as shown above, the alternate spelling, 'snog', is not attested in Wright. This is where the planks of the rickety catwalk break, allowing not a more convincing glimpse of the origins of 'snogging' in the abyss but rather the suggestion that we may fall in by pursuing it farther.