backside vs hindquarters

backside and hindquarters both are nouns.

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

As nouns, backside and hindquarters are synonyms defined as:

backside and hindquarters: the fleshy part of the human body that you sit on

backside (noun)	hindquarters (noun)
the fleshy part of the human body that you sit on	the part of an animal that corresponds to the human buttocks
the side of an object that is opposite its front	the fleshy part of the human body that you sit on