bum vs obtain

bum is a noun but obtain is not a noun.

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

As verbs, obtain is a hypernym of bum; that is, obtain is a word with a broader meaning than bum:

bum (noun)	obtain (noun)
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

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

bum (verb)	obtain (verb)
ask for and get free; be a parasite	receive a specified treatment (abstract)
be lazy or idle	come into possession of
	be valid, applicable, or true