Origin and history of avenge

late 14c., revengen, "avenge oneself," from Old French revengier, revenger, variants of revenchier "take revenge, avenge" (13c., Modern French revancher), from re-, here perhaps an intensive prefix (see re-), + vengier "take revenge," from Latin vindicare "to lay claim to, avenge, punish" (see vindication). Transitive sense of "take vengeance on account of" is from early 15c. Related: Revenged; revenging; revengement.

To avenge is "to get revenge" or "to take vengeance"; it suggests the administration of just punishment for a criminal or immoral act. Revenge seems to stress the idea of retaliation a bit more strongly and implies real hatred as its motivation. ["The Columbia Guide to Standard American English," 1993]

mid-15c., vendicacion, "act of avenging, revenge; assertion of a claim" (senses now obsolete); 1640s as "justification by proof, defense against censure;" from Old French vindicacion "vengeance, revenge" and directly from Latin vindicationem (nominative vindicatio) "act of claiming or avenging," noun of action from past-participle stem of vindicare "lay claim to, assert; claim for freedom, set free; protect, defend; avenge" (related to vindicta "revenge"). This is held to be probably from vim dicare "to show authority," from vim, accusative of vis "force" (see vim) + dicare "to proclaim" (see diction).