foe n.

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.

"of excitement that presages death," from Old English fæge "doomed to die, fated, destined," also "timid, feeble;" and/or from Old Norse feigr, both from Proto-Germanic *faigjo- (source also of Old Saxon fegi, Old Frisian fai, Middle Dutch vege, Middle High German veige "doomed," also "timid," German feige "cowardly"), from the same source as foe. Preserved in Scottish. Sense of "displaying unearthly qualities" and "disordered in the mind (like one about to die)" led to modern ironic sense of "affected."