raininess vs severeness

raininess and severeness both are nouns.

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

As nouns, severeness is a hypernym of raininess; that is, severeness is a word with a broader meaning than raininess:

raininess: (of weather) the badness of the weather
severeness: used of the degree of something undesirable e.g. pain or weather

Other hypernyms of raininess include badness, severity.

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