The Collaborative International Dictionary of English v.0.48:

Exonerate \Ex*on"er*ate\, v. t. [imp. & p. p. Exonerated; p.
   pr. & vb. n. Exonerating.] [L. exoneratus, p. p. of
   exonerare to free from a burden; ex out, from onerare to
   load, onus load. See Onerous.]
   1. To unload; to disburden; to discharge. [Obs.]
      [1913 Webster]

            All exonerate themselves into one common duct.
                                                  --Ray.
      [1913 Webster]

   2. To relieve, in a moral sense, as of a charge, obligation,
      or load of blame resting on one; to clear of something
      that lies upon oppresses one, as an accusation or
      imputation; as, to exonerate one's self from blame, or
      from the charge of avarice. --Burke.
      [1913 Webster]

   3. To discharge from duty or obligation, as a bail.

   Syn: To absolve; acquit; exculpate. See Absolve.
        [1913 Webster]

WordNet (r) 3.0 (2006):

exonerate
    v 1: pronounce not guilty of criminal charges; "The suspect was
         cleared of the murder charges" [syn: acquit, assoil,
         clear, discharge, exonerate, exculpate] [ant:
         convict]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "exonerate":
   absolve, acquit, amnesty, clear, decontaminate, destigmatize,
   disburden, discharge, dismiss, dispense from, exculpate, excuse,
   exempt, exempt from, forgive, free, give absolution,
   grant amnesty to, grant forgiveness, grant immunity,
   grant remission, justify, let go, let off, nonpros, pardon, purge,
   quash the charge, release, remit, set free, shrive, spare,
   vindicate, whitewash, withdraw the charge