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.