1484, "act of avenging, revenge," from L.
vindicationem (nom.
vindicatio) "act of claiming or avenging," from
vindicare "to set free, lay claim to, assert, avenge" (related to
vindicta "revenge"), probably from
vim dicare "to show authority," from
vim, accusative of
vis "force" + root of
dicere "to say" (see
diction). Meaning "justification by proof, defense against censure" is attested from 1647.