rigorousness vs severeness

rigorousness and severeness both are nouns.

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

As nouns, rigorousness and severeness are synonyms defined as:

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

As nouns, rigorousness and severeness are synonyms defined as:

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

rigorousness (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