buttocks vs behind

buttocks and behind both are nouns.

Word	Noun	Adjective	Verb	Adverb
buttocks	Yes	No	No	No
behind	Yes	Yes	No	Yes

As nouns, buttocks and behind are synonyms defined as:

buttocks (noun)	behind (noun)
the fleshy part of the human body that you sit on	the fleshy part of the human body that you sit on

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

buttocks (adverb)	behind (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