ass vs tail end

ass and tail end both are nouns.

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

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

ass (noun)	tail end (noun)
slang for sexual intercourse	the fleshy part of the human body that you sit on
hardy and sure-footed animal smaller and with longer ears than the horse	any projection that resembles the tail of an animal
the fleshy part of the human body that you sit on	the time of the last part of something
a pompous fool