1610s, "vengeful," from Latin vindicta "revenge" (see vindication) + -ive; or perhaps a shortening of vindicative based on the Latin word. From 1620s as "punitive, retributive," rather than personally vengeful or deliberately cruel. Related: Vindictively.
-ness
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).