amniotic sac vs amnion

amniotic sac and amnion both are nouns.

Word	Noun	Adjective	Verb	Adverb
amniotic sac	Yes	No	No	No
amnion	Yes	No	No	No

As nouns, amniotic sac and amnion are synonyms defined as:

amniotic sac and amnion: thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)

Other synonyms of amniotic sac include amnios.

amniotic sac (noun)	amnion (noun)
thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)	thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)