vitelline sac vs sac

vitelline sac and sac both are nouns.

Word	Noun	Adjective	Verb	Adverb
vitelline sac	Yes	No	No	No
sac	Yes	No	No	No

As nouns, sac is a hypernym of vitelline sac; that is, sac is a word with a broader meaning than vitelline sac:

vitelline sac: membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional
sac: a structure resembling a bag in an animal

vitelline sac (noun)	sac (noun)
membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional	a structure resembling a bag in an animal
	a case or sheath especially a pollen sac or moss capsule
	an enclosed space