arse vs posterior

arse and posterior both are nouns.

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

As nouns, arse and posterior are synonyms defined as:

arse (noun)	posterior (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 tooth situated at the back of the mouth

arse (adjective)	posterior (adjective)
	located at or near or behind a part or near the end of a structure
	coming at a subsequent time or stage