posterior vs bum

posterior and bum both are nouns.

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

As nouns, posterior and bum are synonyms defined as:

posterior (noun)	bum (noun)
the fleshy part of the human body that you sit on	the fleshy part of the human body that you sit on
a tooth situated at the back of the mouth	a vagrant
	a person who is deemed to be despicable or contemptible
	person who does no work

posterior (adjective)	bum (adjective)
located at or near or behind a part or near the end of a structure	of very poor quality; flimsy
coming at a subsequent time or stage

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