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.