stern vs rear end

stern and rear end both are nouns.

Word	Noun	Adjective	Verb	Adverb
stern	Yes	Yes	No	No
rear end	Yes	No	No	No

As nouns, stern and rear end are synonyms defined as:

stern (noun)	rear end (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

stern (adjective)	rear end (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