rigour vs severeness

rigour and severeness both are nouns.

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

As nouns, rigour and severeness are synonyms defined as:

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

As nouns, rigour and severeness are synonyms defined as:

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

rigour (noun)	severeness (noun)
something hard to endure	extreme plainness
the quality of being valid and rigorous	excessive sternness
excessive sternness	something hard to endure
	used of the degree of something undesirable e.g. pain or weather