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- (source also of Old English fæhð "enmity," fah "hostile;" German Fehde "feud;" Old Frisian feithe "enmity"). Perhaps from the same PIE source as 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.
1670s, from feud (n.). Related: Feuded; feuding.