harshness vs hardness

harshness and hardness both are nouns.

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

As nouns, harshness and hardness are synonyms defined as:

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

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