severity vs severeness

severity and severeness both are nouns.

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

As nouns, severity and severeness are synonyms defined as:

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

As nouns, severity and severeness are synonyms defined as:

severity and severeness: used of the degree of something undesirable e.g. pain or weather

Other synonyms of severity include badness.

As nouns, severity and severeness are synonyms defined as:

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

As nouns, severity and severeness are synonyms defined as:

Other synonyms of severity include austereness.

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