arse vs bum

arse and bum both are nouns.

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

As nouns, arse and bum are synonyms defined as:

arse (noun)	bum (noun)
vulgar slang for anus	the fleshy part of the human body that you sit on
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

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

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