Source : Webster's Revised Unabridged Dictionary (1913)

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

   2. Unlawfully begotten; born out of wedlock; bastard; as, an
      illegitimate child.

   3. Not legitimately deduced or inferred; illogical; as, an
      illegitimate inference.

   4. Not authorized by good usage; not genuine; spurious; as,
      an illegitimate word.

   {Illegitimate fertilization}, or {Illegitimate union} (Bot.),
      the fertilization of pistils by stamens not of their own
      length, in heterogonously dimorphic and trimorphic
      flowers. --Darwin.

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.

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

Source : WordNet®

illegitimate
     adj 1: contrary to or forbidden by law; "an illegitimate seizure of
            power"; "illicit trade"; "an outlaw strike"; "unlawful
            measures" [syn: {illicit}, {outlaw(a)}, {outlawed}, {unlawful}]
     2: of marriages and offspring; not recognized as lawful [ant: {legitimate}]

illegitimate
     n : the illegitimate offspring of unmarried parents [syn: {bastard},
          {by-blow}, {love child}, {illegitimate child}, {whoreson}]