rigorousness vs rigour

rigorousness and rigour both are nouns.

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

As nouns, rigorousness and rigour are synonyms defined as:

Other synonyms of rigorousness include asperity, grimness, hardship, rigor, rigourousness, severeness, severity.

As nouns, rigorousness and rigour are synonyms defined as:

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

rigorousness (noun)	rigour (noun)
something hard to endure	something hard to endure
excessive sternness	the quality of being valid and rigorous
	excessive sternness