foulness vs severeness

foulness and severeness both are nouns.

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

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

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

Other hypernyms of foulness include badness, severity.

foulness (noun)	severeness (noun)
the attribute of having a strong offensive smell	extreme plainness
(of weather) the badness of the weather	excessive sternness
a state characterized by foul or disgusting dirt and refuse	something hard to endure
disgusting wickedness and immorality	used of the degree of something undesirable e.g. pain or weather