severeness vs raininess

severeness and raininess both are nouns.

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

As nouns, raininess is a hyponym of severeness; that is, raininess is a word with a more specific, narrower meaning than severeness:

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

Other hyponyms of severeness include foulness, distressfulness, seriousness.

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