feudyoudaoicibaDictYouDict[feud 词源字典]
feud: [13] Feud signifies etymologically the ‘condition of being a foe’. It was borrowed from Old French fede or feide, and originally meant simply ‘hostility’; the modern sense ‘vendetta’ did not develop until the 15th century. The Old French word in turn was a borrowing from Old High German fēhida. This was a descendant of a prehistoric Germanic *faikhithō, a compound based on *faikh- ‘hostility’ (whence English foe).

Old English had a parallel descendant, fāhthu ‘enmity’, which appears to have died out before the Middle English period. It is not clear how the original Middle English form fede turned into modern English feud (the first signs of which began to appear in the late 16th century).
=> foe[feud etymology, feud origin, 英语词源]
feud (n.)youdaoicibaDictYouDict
c. 1300, fede "enmity, hatred, hostility," northern English and Scottish, ultimately (via an unrecorded Old English word or Old French fede, faide "war, raid, hostility, hatred, enmity, feud, (legal) vengeance," which is from Germanic) from Proto-Germanic *faihitho (compare Old High German fehida "contention, quarrel, feud"), noun of state from adjective *faiho- (cognates: Old English fæhð "enmity," fah "hostile;" German Fehde "feud;" Old Frisian feithe "enmity").

This is from PIE root *peig- (2), also *peik- "evil-minded, hostile" (see foe). Sense of "vendetta" is early 15c. Alteration of spelling in 16c. is unexplained. Meaning "state of hostility between families or clans" is from 1580s.
feud (v.)youdaoicibaDictYouDict
1670s, from feud (n.). Related: Feuded; feuding.