stern vs backside

stern and backside both are nouns.

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

As nouns, stern and backside are synonyms defined as:

stern (noun)	backside (noun)
the rear part of a ship	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

stern (adjective)	backside (adjective)
severe and unremitting in making demands
not to be placated or appeased or moved by entreaty
of a stern or strict bearing or demeanor; forbidding in aspect
severely simple