harshness vs rigourousness

harshness and rigourousness both are nouns.

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

As nouns, harshness and rigourousness are synonyms defined as:

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

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