sac vs cavity

sac and cavity both are nouns.

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

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

Other hypernyms of sac include bodily cavity, cavum.

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

Other hypernyms of sac include enclosed space.

sac (noun)	cavity (noun)
a structure resembling a bag in an animal	(anatomy) a natural hollow or sinus within the body
a case or sheath especially a pollen sac or moss capsule	a sizeable hole (usually in the ground)
an enclosed space	soft decayed area in a tooth; progressive decay can lead to the death of a tooth
	space that is surrounded by something