| Noun | 1. | illegitimate - the illegitimate offspring of unmarried parentsoffspring, progeny, issue - the immediate descendants of a person; "she was the mother of many offspring"; "he died without issue" | |
| Adj. | 1. | illegitimate - contrary to or forbidden by law; "an illegitimate seizure of power"; "illicit trade"; "an outlaw strike"; "unlawful measures"illegal - prohibited by law or by official or accepted rules; "an illegal chess move" | |
| 2. | illegitimate - of marriages and offspring; not recognized as lawfulillegal - prohibited by law or by official or accepted rules; "an illegal chess move" invalid - having no cogency or legal force; "invalid reasoning"; "an invalid driver's license" legitimate - of marriages and offspring; recognized as lawful | |