mailbag vs pouch

mailbag and pouch both are nouns.

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

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

mailbag (noun)	pouch (noun)
letter carrier's shoulder bag	a small or medium size container for holding or carrying things
pouch used in the shipment of mail	(anatomy) saclike structure in any of various animals (as a marsupial or gopher or pelican)
	an enclosed space

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