loon vs bum

loon and bum both are nouns.

Word	Noun	Adjective	Verb	Adverb
loon	Yes	No	No	No
bum	Yes	Yes	Yes	No

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

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

loon (noun)	bum (noun)
large somewhat primitive fish-eating diving bird of the Northern Hemisphere having webbed feet placed far back; related to the grebes	the fleshy part of the human body that you sit on
a worthless lazy fellow	a vagrant
a person with confused ideas; incapable of serious thought	a person who is deemed to be despicable or contemptible
	person who does no work

loon (adjective)	bum (adjective)
	of very poor quality; flimsy

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