The only free and comprehensive online etymological dictionary of the Spanish language
vengar (Verb) "to avenge"
12th cent. From Latin vindicare 'id.' From vindex "defender," "avenger." A compound from Proto-Italic *wīm, accusative of *wīs "strength," and *-dik-s "saying" (see -ez). From Proto-Indo-European *u̯iH-s "strength," from the same root as -vir.
Indo-European
Romance
Asturian vengar, Portuguese vingar, Catalan venjar, French venger, Italian vendicare, Aromanian vindic, Romanian vindeca
Hellenic
Ancient Greek ἴ̄ς (hís) "power"
Indo-Iranian
Sanskrit váyas- "strength"