'avengeress' originates from English, specifically formed from 'avenger' + the feminine suffix '-ess', where the suffix '-ess' came from Old French '-esse' (ultimately from Latin elements meaning 'female').

'avenger' derives from Old French 'avengier' (to avenge), ultimately from Latin Vulgar/Latin roots related to 'vindicāre' (to claim, avenge). The modern English 'avenger' developed through Middle English, and the feminine form 'avengeress' was later created by adding the suffix '-ess'.

Initially it meant 'a woman who takes vengeance', and that primary sense has been retained; however, the explicitly marked feminine form is now rare/archaic and often replaced by gender-neutral terms like 'avenger.'