backside vs behind

backside and behind both are nouns.

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

As nouns, backside and behind are synonyms defined as:

backside (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
the side of an object that is opposite its front

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

backside (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