The Collaborative International Dictionary of English v.0.48:

Illegitimate \Il`le*git"i*mate\, v. t. [imp. & p. p.
   Illegitimated; p. pr. & vb. n. Illegitimating.]
   To render illegitimate; to declare or prove to be born out of
   wedlock; to bastardize; to illegitimatize.
   [1913 Webster]

         The marriage should only be dissolved for the future,
         without illegitimating the issue.        --Bp. Burnet.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Illegitimate \Il`le*git"i*mate\, a.
   1. Not according to law; not regular or authorized; unlawful;
      improper.
      [1913 Webster]

   2. Unlawfully begotten; born out of wedlock; bastard; as, an
      illegitimate child.
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   3. Not legitimately deduced or inferred; illogical; as, an
      illegitimate inference.
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   4. Not authorized by good usage; not genuine; spurious; as,
      an illegitimate word.
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   Illegitimate fertilization, or Illegitimate union (Bot.),
      the fertilization of pistils by stamens not of their own
      length, in heterogonously dimorphic and trimorphic
      flowers. --Darwin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

illegitimate
    adj 1: contrary to or forbidden by law; "an illegitimate seizure
           of power"; "illicit trade"; "an outlaw strike"; "unlawful
           measures" [syn: illegitimate, illicit, outlaw(a),
           outlawed, unlawful]
    2: of marriages and offspring; not recognized as lawful [ant:
       legitimate]
    n 1: the illegitimate offspring of unmarried parents [syn:
         bastard, by-blow, love child, illegitimate child,
         illegitimate, whoreson]