The question is on the words with a word-final "ght", such as in "fight" and "wight", which are quite mysterious, I hope to know the connections among these "ght" words.
The question comes from the fact that I just don't understand the "t" in the PGmc origin "nakht-", "fekhtanan" and "wekhtiz" stand for, because I can not find the descriptions about the function or meaning of the PGmc or PIE morpheme "t".
So the ultimate question is: What is the historical function about the "t" mentioned in the words(with these old language words) above?
O.E. niht (W.Saxon neaht, Anglian næht, neht) "night, darkness;" the vowel indicating that the modern word derives from oblique cases (gen. nihte, dat. niht), from P.Gmc. *nakht- (cf. O.S., O.H.G. naht, O.Fris., Du., nacht, Ger. Nacht, O.N. natt, Goth. nahts), from PIE *nekwt- "night" (cf. Gk. nuks "a night," L. nox, O.Ir. nochd, Skt. naktam "at night," Lith. naktis "night," O.C.S. nosti, Rus. noch', Welsh henoid "tonight"), according to Watkins, probably from a verbal root *neg- "to be dark, be night." For spelling with -gh- see fight.
O.E. feohtan "to fight" (class III strong verb; past tense feaht, pp. fohten), from P.Gmc. *fekhtanan (cf. O.H.G. fehtan, Ger. fechten, M.Du., Du. vechten, O.Fris. fiuhta "to fight"), from PIE *pek- "to pluck out" (wool or hair), apparently with a notion of "pulling roughly" (cf. Gk. pekein "to comb, shear," pekos "fleece, wool;" Pers. pashm "wool, down," L. pectere "to comb," Skt. paksman- "eyebrows, hair").
Spelling substitution of -gh- for a "hard H" sound was a Middle English scribal habit, especially before -t-. In some late Old English examples, the middle consonant was represented by a yogh. To fight back "resist" is recorded from 1890.
O.E. wiht "living being, creature," from P.Gmc. *wekhtiz (cf. O.S. wiht "thing, demon," Du. wicht "a little child," O.H.G. wiht "thing, creature, demon," Ger. Wicht "creature, infant," O.N. vettr "thing, creature," Swed. vätte "spirit of the earth, gnome," Goth. waihts "something").
The only apparent cognate outside Gmc. is O.C.S. vešti "a thing." Not related to the Isle of Wight, which is from L. Vectis (c.150), originally Celtic, possibly meaning "place of the division."