tail end vs posterior

tail end and posterior both are nouns.

Word	Noun	Adjective	Verb	Adverb
tail end	Yes	No	No	No
posterior	Yes	Yes	No	No

As nouns, tail end and posterior are synonyms defined as:

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

tail end (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
any projection that resembles the tail of an animal	a tooth situated at the back of the mouth
the time of the last part of something

tail end (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