behind vs tail end

behind and tail end both are nouns.

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

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

behind (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

behind (adjective)	tail end (adjective)
having the lower score or lagging position in a contest

behind (adverb)	tail end (adverb)
in or to or toward the rear
remaining in a place or condition that has been left or departed from
in debt
in or into an inferior position
showing a time that is earlier than the actual time