foulness vs severity

foulness and severity both are nouns.

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

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

Other hypernyms of foulness include badness, severeness.

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