late Old English (c.1050), wyrre, werre, from Old North French werre "war" (Modern French guerre), from Frankish *werra, from Proto-Germanic *werso (cf. Old Saxon werran, Old High German werran, German verwirren "to confuse, perplex"). Cognates suggest the original sense was "to bring into confusion."
Spanish, Portuguese, and Italian guerra are from the same source; Romanic peoples turned to Germanic for a word to avoid Latin bellum because its form tended to merge with bello- "beautiful." There was no common Germanic word for "war" at the dawn of historical times. Old English had many poetic words for "war" (wig, guð, heaðo, hild, all common in personal names), but the usual one to translate Latin bellum was gewin "struggle, strife" (related to win).
First record of war time is late 14c. Warpath (1775) is originally in reference to North American Indians, as are war-whoop (1761), war-paint (1826), and war-dance (1757). War crime first attested 1906. War chest is attested from 1901; now usually figurative. War games translates German Kriegspiel (see kriegspiel).