Etymology
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avenge (v.)
"vindicate by inflicting pain or evil on the wrongdoer," late 14c., from Anglo-French avenger, Old French avengier, from a- "to" (see ad-) + vengier "take revenge" (Modern French venger), from Latin vindicare "to claim, avenge, punish" (see vindication). See revenge (v.) for distinction of use. Related: Avenged; avenging. As a noun to go with it, 16c. English tried avenge, avengeance, avengement, avenging.
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avenger (n.)
1530s, agent noun from avenge (v.). Spenser (1596) has fem. form avengeress.
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*deik- 
Proto-Indo-European root meaning "to show," also "pronounce solemnly," "also in derivatives referring to the directing of words or objects" [Watkins].

It forms 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 is the hypothetical source of/evidence for its existence is provided by: Sanskrit dic- "point out, show;" Greek deiknynai "to show, to prove," dike "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."
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venge (v.)
"avenge," c. 1300, from Old French vengier "revenge, avenge, punish," from Latin vindicare "avenge, vindicate" (see vindication). Related: Venged; venging.
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revenge (v.)

late 14c., revengen, "avenge oneself," from Old French revengier, revenger, variants of revenchier "take revenge, avenge" (13c., Modern French revancher), from re-, here perhaps an intensive prefix (see re-), + vengier "take revenge," from Latin vindicare "to lay claim to, avenge, punish" (see vindication). Transitive sense of "take vengeance on account of" is from early 15c. Related: Revenged; revenging; revengement.

To avenge is "to get revenge" or "to take vengeance"; it suggests the administration of just punishment for a criminal or immoral act. Revenge seems to stress the idea of retaliation a bit more strongly and implies real hatred as its motivation. ["The Columbia Guide to Standard American English," 1993]
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wreak (v.)

Old English wrecan "avenge," originally "to drive, drive out, punish" (class V strong verb; past tense wræc, past participle wrecen), from Proto-Germanic *wrekanan (source also of Old Saxon wrekan, Old Norse reka, Old Frisian wreka, Middle Dutch wreken "to drive, push, compel, pursue, throw," Old High German rehhan, German rächen "to avenge," Gothic wrikan "to persecute"), from PIE root *wreg- "to push, shove, drive, track down" (see urge (v.)). Meaning "inflict or take vengeance," with on, is recorded from late 15c.; that of "inflict or cause (damage or destruction)" is attested from 1817. Compare wrack (v.). Related: Wreaked; wreaking.

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vindicate (v.)
1620s, "to avenge or revenge," from Latin vindicatus, past participle of vindicare "to stake a claim; to liberate; to act as avenger" (see vindication). Meaning "to clear from censure or doubt, by means of demonstration" is recorded from 1630s. Related: Vindicated, vindicating.
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vengeance (n.)

c. 1300, 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).

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]
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vindication (n.)

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.

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right (v.)

Old English rihtan "to straighten (a path); rule, set up, set right, amend; guide, govern; restore, replace," from riht (adj.); see right (adj.1). Compare Old Norse retta "to straighten," Old Saxon rihtian, Old Frisian riuchta, German richten, Gothic garaihtjan.

From late 14c. as "avenge or redress" (a wrong or injury). The meaning "bring (a ship) back to an upright position" is by 1745; the sense of "recover one's balance or footing" is by 1805. The meaning "restore (something) to proper position after a fall, etc." is by 1823. Related: Righted; righting.

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