illegitimacy vs bastardy

illegitimacy and bastardy both are nouns.

Word	Noun	Adjective	Verb	Adverb
illegitimacy	Yes	No	No	No
bastardy	Yes	No	No	No

As nouns, illegitimacy and bastardy are synonyms defined as:

illegitimacy and bastardy: the status of being born to parents who were not married

Other synonyms of illegitimacy include bar sinister.

illegitimacy (noun)	bastardy (noun)
unlawfulness by virtue of not being authorized by or in accordance with law	the status of being born to parents who were not married
the status of being born to parents who were not married