rigourousness vs severeness

rigourousness and severeness both are nouns.

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

As nouns, rigourousness and severeness are synonyms defined as:

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

As nouns, rigourousness and severeness are synonyms defined as:

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

rigourousness (noun)	severeness (noun)
something hard to endure	extreme plainness
excessive sternness	excessive sternness
	something hard to endure
	used of the degree of something undesirable e.g. pain or weather