posterior vs arse

posterior and arse both are nouns.

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

As nouns, posterior and arse are synonyms defined as:

posterior (noun)	arse (noun)
the fleshy part of the human body that you sit on	vulgar slang for anus
a tooth situated at the back of the mouth	the fleshy part of the human body that you sit on

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