sac vs cavum

sac and cavum both are nouns.

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

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

Other hypernyms of sac include bodily cavity, cavity.

sac (noun)	cavum (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
an enclosed space