vindictive adj.

late 15c., "act of avenging, revenge," 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"), probably from vim dicare "to show authority," from vim, accusative of vis "force" (see vim) + dicare "to proclaim" (from PIE root *deik- "to show," also "pronounce solemnly," and see diction). Meaning "justification by proof, defense against censure" is attested from 1640s.

word-forming element making adjectives from verbs, meaning "pertaining to, tending to; doing, serving to do," in some cases from Old French -if, but usually directly from Latin adjectival suffix -ivus (source also of Italian and Spanish -ivo). In some words borrowed from French at an early date it has been reduced to -y (as in hasty, tardy).