enclosed space vs sac

enclosed space and sac both are nouns.

Word	Noun	Adjective	Verb	Adverb
enclosed space	Yes	No	No	No
sac	Yes	No	No	No

As nouns, sac is a hyponym of enclosed space; that is, sac is a word with a more specific, narrower meaning than enclosed space:

Other hyponyms of enclosed space include hollow, pocket, pouch, sack.

enclosed space (noun)	sac (noun)
space that is surrounded by something	a structure resembling a bag in an animal
	a case or sheath especially a pollen sac or moss capsule
	an enclosed space