rigour vs severity

rigour and severity both are nouns.

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

As nouns, rigour and severity are synonyms defined as:

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

As nouns, rigour and severity are synonyms defined as:

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