amnion vs amniotic sac

amnion and amniotic sac both are nouns.

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

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

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

Other synonyms of amnion include amnios.

amnion (noun)	amniotic sac (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)