The Collaborative International Dictionary of English v.0.48:

disqualify \dis*qual"i*fy\ (d[i^]s*kw[o^]l"[i^]*f[imac]), v. t.
   [imp. & p. p. Disqualified (d[i^]s*kw[o^]l"[i^]*f[imac]d);
   p. pr. & vb. n. Disqualifying.]
   1. To deprive of the qualities or properties necessary for
      any purpose; to render unfit; to incapacitate; -- with for
      or from before the purpose, state, or act.
      [1913 Webster]

            My common illness disqualifies me for all
            conversation; I mean my deafness.     --Swift.
      [1913 Webster]

            Me are not disqualified by their engagements in
            trade from being received in high society.
                                                  --Southey.
      [1913 Webster]

   2. To deprive of some power, right, or privilege, by positive
      restriction; to disable; to debar legally; as, a
      conviction of perjury disqualifies a man to be a witness.
      [1913 Webster]

WordNet (r) 3.0 (2006):

disqualify
    v 1: make unfit or unsuitable; "Your income disqualifies you"
         [syn: disqualify, unfit, indispose] [ant: dispose,
         qualify]
    2: declare unfit; "She was disqualified for the Olympics because
       she was a professional athlete" [ant: qualify]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "disqualify":
   bar, bate, close out, debar, disable, disenable, eliminate, except,
   exclude, incapacitate, invalidate, make impossible, prohibit,
   reject, rule out, suspend, turn away, turn down, unfit