severe vs severity

severe is not a noun while severity is a noun.

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

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

severe (adjective)	severity (adjective)
causing fear or anxiety by threatening great harm
intensely or extremely bad or unpleasant in degree or quality
severely simple
very strong or vigorous
very bad in degree or extent
unsparing and uncompromising in discipline or judgment