rear end vs tail end

rear end and tail end both are nouns.

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

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

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

rear end (noun)	tail end (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
	the time of the last part of something