1. (a.) Unlawfully begotten; as, an illegitimate child or illegitimate gains.

2. (a.) Not according to law; not regular or authorized; unlawful; improper.

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

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

5. (v. t.) To render illegitimate; to declare or prove to be born out of wedlock; to bastardize; to illegitimatize.