vesicle vs sac

vesicle and sac both are nouns.

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

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

vesicle: a small anatomically normal sac or bladderlike structure (especially one containing fluid)
sac: a structure resembling a bag in an animal

vesicle (noun)	sac (noun)
a small anatomically normal sac or bladderlike structure (especially one containing fluid)	a structure resembling a bag in an animal
	a case or sheath especially a pollen sac or moss capsule
	an enclosed space