(1):

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

(2):

(a.) Unlawfully begotten; born out of wedlock; bastard; as, an illegitimate child.

(3):

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

(4):

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

(5):

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