rigour vs rigorousness

rigour and rigorousness both are nouns.

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

As nouns, rigour and rigorousness are synonyms defined as:

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

As nouns, rigour and rigorousness are synonyms defined as:

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

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