hare n.

Old English hergian "make war, lay waste, ravage, plunder," the word used in the Anglo-Saxon Chronicle for what the Vikings did to England, from Proto-Germanic *harjon (source also of Old Frisian urheria "lay waste, ravage, plunder," Old Norse herja "to make a raid, to plunder," Old Saxon and Old High German herion, German verheeren "to destroy, lay waste, devastate"). This is literally "to overrun with an army," from Proto-Germanic *harjan "an armed force" (source also of Old English here, Old Norse herr "crowd, great number; army, troop," Old Saxon and Old Frisian heri, Dutch heir, Old High German har, German Heer, Gothic harjis "a host, army").

The Germanic words come from PIE root *korio- "war" also "war-band, host, army" (source also of Lithuanian karas "war, quarrel," karias "host, army;" Old Church Slavonic kara "strife;" Middle Irish cuire "troop;" Old Persian kara "host, people, army;" Greek koiranos "ruler, leader, commander"). Weakened sense of "worry, goad, harass" is from c. 1400. Related: Harried; harrying.

1670s (harum-starum), probably a rhyming compound of obsolete hare (v.) "harry" + scare (v.), with 'um as a reduced form of them, the whole perhaps meant to be mock Latin. As an adjective from 1751; as a noun, "reckless person," from 1784.