keister vs posterior

keister and posterior both are nouns.

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

As nouns, keister and posterior are synonyms defined as:

keister and posterior: the fleshy part of the human body that you sit on

keister (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 tooth situated at the back of the mouth

keister (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