pouch vs sac

pouch and sac both are nouns.

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

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

pouch: (anatomy) saclike structure in any of various animals (as a marsupial or gopher or pelican)
sac: a structure resembling a bag in an animal

As nouns, pouch and sac are synonyms defined as:

Other synonyms of pouch include pocket, sack.

pouch (noun)	sac (noun)
a small or medium size container for holding or carrying things	a structure resembling a bag in an animal
(anatomy) saclike structure in any of various animals (as a marsupial or gopher or pelican)	a case or sheath especially a pollen sac or moss capsule
an enclosed space	an enclosed space

pouch (verb)	sac (verb)
swell or protrude outwards
put into a small bag
send by special mail that goes through diplomatic channels