The Collaborative International Dictionary of English v.0.48:

Disavow \Dis`a*vow"\, v. t. [imp. & p. p. Disavowed; p. pr. &
   vb. n. Disavowing.] [F. d['e]savouer; pref. d['e]s- (L.
   dis-) + avouer to avow. See Avow, and cf. Disavouch.]
   1. To refuse strongly and solemnly to own or acknowledge; to
      deny responsibility for, approbation of, and the like; to
      disclaim; to disown; as, he was charged with embezzlement,
      but he disavows the crime.
      [1913 Webster]

            A solemn promise made and disavowed.  --Dryden.
      [1913 Webster]

   2. To deny; to show the contrary of; to disprove.
      [1913 Webster]

            Yet can they never
            Toss into air the freedom of my birth,
            Or disavow my blood Plantagenet's.    --Ford.
      [1913 Webster]

WordNet (r) 3.0 (2006):

disavow
    v 1: refuse to acknowledge; disclaim knowledge of;
         responsibility for, or association with; "Her husband
         disavowed her after 30 years of marriage and six children"
         [ant: avouch, avow]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "disavow":
   abjure, assert the contrary, back down, back out, backwater, belie,
   climb down, contest, contradict, contravene, controvert, counter,
   crawfish out, cross, deny, disaffirm, disallow, disclaim, disown,
   disprove, dispute, eat crow, eat humble pie, forswear, gainsay,
   impugn, join issue upon, negate, negative, not accept, not admit,
   nullify, oppose, recant, refuse to admit, refute, renege, renounce,
   repudiate, retract, revoke, swallow, take back, take issue with,
   unsay, withdraw