illegitimate child vs bastard

illegitimate child and bastard both are nouns.

Word	Noun	Adjective	Verb	Adverb
illegitimate child	Yes	No	No	No
bastard	Yes	Yes	No	No

As nouns, illegitimate child and bastard are synonyms defined as:

illegitimate child and bastard: the illegitimate offspring of unmarried parents

Other synonyms of illegitimate child include by-blow, illegitimate, love child, whoreson.

illegitimate child (noun)	bastard (noun)
the illegitimate offspring of unmarried parents	derogatory term for a variation that is not genuine; something irregular or inferior or of dubious origin
	insulting terms of address for people who are stupid or irritating or ridiculous
	the illegitimate offspring of unmarried parents

illegitimate child (adjective)	bastard (adjective)
	fraudulent; having a misleading appearance