buns vs posterior

buns and posterior both are nouns.

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

As nouns, buns and posterior are synonyms defined as:

buns (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

buns (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