#1 illegitimate s. [illicit, outlaw, outlawed, unlawful] contrary to or forbidden by law; "an illegitimate seizure of power"; "illicit trade"; "an outlaw strike"; "unlawful measures". wn #2 illegitimate n. [bastard, by-blow, love child, illegitimate child, whoreson] the illegitimate offspring of unmarried parents. wn #3 illegitimate a. of marriages and offspring; not recognized as lawful. wn