bum vs posterior

bum and posterior both are nouns.

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

As nouns, bum and posterior are synonyms defined as:

bum (noun)	posterior (noun)
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 tooth situated at the back of the mouth
a person who is deemed to be despicable or contemptible
person who does no work

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

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