rigorousness vs harshness

rigorousness and harshness both are nouns.

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

As nouns, rigorousness and harshness are synonyms defined as:

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

rigorousness (noun)	harshness (noun)
something hard to endure	the quality of being harsh or rough or grating to the senses
excessive sternness	excessive sternness
	the roughness of a substance that causes abrasions
	the quality of being cruel and causing tension or annoyance