posterior vs fundament

posterior and fundament both are nouns.

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

As nouns, posterior and fundament are synonyms defined as:

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

posterior (noun)	fundament (noun)
the fleshy part of the human body that you sit on	lowest support of a structure
a tooth situated at the back of the mouth	the fleshy part of the human body that you sit on
	the fundamental assumptions from which something is begun or developed or calculated or explained

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