couch potato vs bum

couch potato and bum both are nouns.

Word	Noun	Adjective	Verb	Adverb
couch potato	Yes	No	No	No
bum	Yes	Yes	Yes	No

As nouns, bum is a hypernym of couch potato; that is, bum is a word with a broader meaning than couch potato:

couch potato: an idler who spends much time on a couch (usually watching television)
bum: person who does no work

Other hypernyms of couch potato include do-nothing, idler, layabout, loafer.

couch potato (noun)	bum (noun)
an idler who spends much time on a couch (usually watching television)	the fleshy part of the human body that you sit on
	a vagrant
	a person who is deemed to be despicable or contemptible
	person who does no work

couch potato (adjective)	bum (adjective)
	of very poor quality; flimsy

couch potato (verb)	bum (verb)
	ask for and get free; be a parasite
	be lazy or idle