What does "-t" in "bight" mean? [closed]
Wiktionary says, that "-t" in "bight" is a variant of "-th" suffix (bight = bought = bough + t) but I think, that "-t" in "bight" is an Old English past participle ending of "bow". Is my hypothesis reasonable?
No, that is not possible
As you’ve already discovered, the verb bow and the noun bight both derive from the Proto-Indo-European (verbal) root *bʰeu̯gʰ- ‘bend, curve’, but they are different formations.
The suffixes
Wiktionary is correct that the suffix in bight is the -t which is an alternative form of -th. This suffix was in Proto-Germanic *-þiz, inherited from PIE *-ti-s (where *-s is the nominative singular masculine ending, so the suffix itself is *-ti-). These *-ti- stems are exceedingly common in PIE, and they generally form abstract nouns from verbal roots.
The past participle suffix, on the other hand, was in PIE *-tó-s, in Germanic *-þaz alternating with *-taz in the same way that *-tiz and *-þiz alternated depending on the preceding sound. The past participle, if formed to the same root, would have been **buhtaz in PG, but as it happens, I don’t think that form existed. The verb *beugana- ‘bow, bend’ is a strong verb in Germanic, and as such, it forms its past participle with the other inherited past participle suffix, *-naz (from PIE *-nó-s).
There is a different verb from a PIE root which is either homophonic or actually just the same root, namely PG *būgjana- ‘deal, buy’ – and that verb is weak and forms its past participle with the dental suffix: *buhtaz, the direct ancestor of bought in current English.
How the suffixes develop after Proto-Germanic
This indicates (indirectly, but also correctly, I can tell you) that PG *buhtiz and *buhtaz develop differently later on.
They do so because of two roughly opposite developments: i-mutation, whereby a vowel develops into a higher, more fronted version of itself if there is an /i/ in the following syllable; and a-mutation, whereby a vowel develops into a lower, vowel if there is an /a/ in the following syllable.
For the vowel /u/ in Germanic languages, this means a development from /u/ to /y/ (as in French une) with i-mutation, and a development from /u/ to /o/ with a-mutation. The sound /y/ existed in Old English, but was lost in Middle English when it merged with /i/, so for present-day English purposes, you could say that i-mutation turned /u/ into /i/.
The West Germanic languages all lost final consonants, then all unstressed final syllables very early on – before Old English – but i- and a-mutation had already happened by that time, and their results remained in place after the final syllables that caused them were lost. That means our two words here developed thus:
- *buhtiz first became *byhtiz, then *byhti, then byht (the actual word as attested in Old English), and then in Middle English biht (also spelt biȝt and half a dozen other ways) and in Modern English bight
- *buhtaz first became *bohtaz, then *bohta, then boht (the Old English form). The sequence /oht/ was somewhat labile and didn’t develop very regularly during the Great Vowel Shift; in most cases, as in this case, it ended up as /ɔːt/ in Modern English
tl;dr / Conclusion
As should be clear now, bight cannot come from any form with an inherited past participle suffix (PIE *-tó-s, PG *-þaz/-taz, Eng. _-t/-ed) because it shows the clear effect of i-mutation, which the past participle suffix does not cause. It fits instead with the abstract noun suffix (PIE *-ti-s, PG *-þiz/-tiz, Eng. -th/-t), which has an /i/ in it and does cause i-mutation.
Conversely, the form bought does fit with an inherited past participle suffix because it shows the effect of a-mutation, which the abstract noun suffix does not cause.