sternness vs hardness

sternness and hardness both are nouns.

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

As nouns, hardness is a hyponym of sternness; that is, hardness is a word with a more specific, narrower meaning than sternness:

sternness (noun)	hardness (noun)
uncompromising resolution	a quality of water that contains dissolved mineral salts that prevent soap from lathering
the quality (as of scenery) being grim and gloomy and forbidding	the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale
	the quality of being difficult to do
	devoid of passion or feeling; hardheartedness
	excessive sternness