sternness vs stern

sternness and stern both are nouns.

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

sternness (noun)	stern (noun)
uncompromising resolution	the rear part of a ship
the quality (as of scenery) being grim and gloomy and forbidding	the fleshy part of the human body that you sit on

sternness (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