The Collaborative International Dictionary of English v.0.48:

Disown \Dis*own"\, v. t. [imp. & p. p. Disowned; p. pr. & vb.
   n. Disowning.]
   1. To refuse to own or acknowledge as belonging to one's
      self; to disavow or deny, as connected with one's self
      personally; as, a parent can hardly disown his child; an
      author will sometimes disown his writings.
      [1913 Webster]

   2. To refuse to acknowledge or allow; to deny.
      [1913 Webster]

            Then they, who brother's better claim disown,
            Expel their parents, and usurp the throne. --Dryden.

   Syn: To disavow; disclaim; deny; abnegate; renounce;
        disallow.
        [1913 Webster]

WordNet (r) 3.0 (2006):

disown
    v 1: prevent deliberately (as by making a will) from inheriting
         [syn: disinherit, disown] [ant: bequeath, leave,
         will]
    2: cast off; "She renounced her husband"; "The parents
       repudiated their son" [syn: disown, renounce,
       repudiate]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "disown":
   abjure, assert the contrary, back down, back out, backwater, belie,
   brush aside, chuck, chuck out, climb down, contemn, contest,
   contradict, contravene, controvert, counter, crawfish out, cross,
   cut off, decline, deny, despise, disaffirm, disallow, disapprove,
   disavow, discard, disclaim, discount, disdain, disendow,
   disherison, disinherit, dismiss, dispossess, disprove, dispute,
   disregard, disseise, eat crow, eat humble pie, evict, except,
   exclude, expropriate, foreclose, forswear, gainsay, ignore, impugn,
   join issue upon, not accept, not admit, nullify, oppose, pass by,
   pass up, push aside, rebuff, recant, refuse, refuse to admit,
   refuse to consider, refute, reject, renege, renounce, repel,
   repudiate, repulse, retract, revoke, scout, shove away, spurn,
   swallow, take back, take issue with, throw away, throw out,
   turn away, turn out, unsay, waive, withdraw