The Collaborative International Dictionary of English v.0.48:

Avenge \A*venge"\, v. t. [imp. & p. p. Avenged (?); p. pr. &
   vb. n. Avenging (?).] [OF. avengier; L. ad + vindicare to
   lay claim to, to avenge, revenge. See Vengeance.]
   1. To take vengeance for; to exact satisfaction for by
      punishing the injuring party; to vindicate by inflicting
      pain or evil on a wrongdoer.
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            He will avenge the blood of his servants. --Deut.
                                                  xxxii. 43.
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            Avenge, O Lord, thy slaughtered saints, whose bones
            Lie scattered on the Alpine mountains cold.
                                                  --Milton.
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            He had avenged himself on them by havoc such as
            England had never before seen.        --Macaulay.
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   2. To treat revengefully; to wreak vengeance on. [Obs.]
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            Thy judgment in avenging thine enemies. --Bp. Hall.
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   Syn: To Avenge, Revenge.

   Usage: To avenge is to inflict punishment upon evil doers in
          behalf of ourselves, or others for whom we act; as, to
          avenge one's wrongs; to avenge the injuries of the
          suffering and innocent. It is to inflict pain for the
          sake of vindication, or retributive justice. To
          revenge is to inflict pain or injury for the
          indulgence of resentful and malicious feelings. The
          former may at times be a duty; the latter is one of
          the worst exhibitions of human character.
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                I avenge myself upon another, or I avenge
                another, or I avenge a wrong. I revenge only
                myself, and that upon another.    --C. J. Smith.
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WordNet (r) 3.0 (2006):

avenged
    adj 1: for which vengeance has been taken; "an avenged injury"
           [ant: unavenged]