buttocks vs stern

buttocks and stern both are nouns.

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

As nouns, buttocks and stern are synonyms defined as:

buttocks (noun)	stern (noun)
the fleshy part of the human body that you sit on	the rear part of a ship
	the fleshy part of the human body that you sit on

buttocks (adjective)	stern (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