hardness vs harshness

hardness and harshness both are nouns.

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

As nouns, hardness and harshness are synonyms defined as:

Other synonyms of hardness include inclemency, rigor, rigorousness, rigour, rigourousness, severeness, severity, stiffness.

hardness (noun)	harshness (noun)
a quality of water that contains dissolved mineral salts that prevent soap from lathering	the quality of being harsh or rough or grating to the senses
the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale	excessive sternness
the quality of being difficult to do	the roughness of a substance that causes abrasions
devoid of passion or feeling; hardheartedness	the quality of being cruel and causing tension or annoyance
excessive sternness