mid-15c., vendicacion, "act of avenging, revenge; assertion of a claim" (senses now obsolete); 1640s as "justification by proof, defense against censure;" 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"). This is held to be probably from vim dicare "to show authority," from vim, accusative of vis "force" (see vim) + dicare "to proclaim" (see diction).

c. 1300, vengeaunce, "retribution, punishment, revenge," from Anglo-French vengeaunce, Old French vengeance, venjance "revenge, retribution" (12c.), from vengier "take revenge," from Latin vindicare "assert a claim, claim as one's own; avenge, punish" (see vindicate). Alternative vengement is attested from mid-14c.

Vengeance is mine, ... saith the Lord. Therefore if thine enemy hunger, feed him; if he thirst, give him drink; for in so doing thou shalt heap coals of fire upon his head. [Paul to the Romans, xii:19-20]

1640s, "serving to justify, tending to vindicate;" 1650s, "avenging, punitive;" from vindicate + -ory.

Proto-Indo-European root meaning "to show," also "pronounce solemnly," "also in derivatives referring to the directing of words or objects" [Watkins].

It might form all or part of: abdicate; abdication; addict; adjudge; apodictic; avenge; benediction; betoken; condition; contradict; contradiction; dedicate; deictic; deixis; dictate; diction; dictionary; dictum; digit; disk; ditto; ditty; edict; Eurydice; index; indicate; indication; indict; indiction; indictive; indite; interdict; judge; judicial; juridical; jurisdiction; malediction; malison; paradigm; policy (n.2) "written insurance agreement;" preach; predicament; predicate; predict; prejudice; revenge; soi-disant; syndic; teach; tetchy; theodicy; toe; token; valediction; vendetta; verdict; veridical; vindicate; vindication; voir dire.

It might also be the source of: Sanskrit dic- "point out, show;" Greek deiknynai "to show, to prove," dikē "custom, usage;" Latin dicere "speak, tell, say," digitus "finger," Old High German zeigon, German zeigen "to show," Old English teon "to accuse," tæcan "to teach."