invalid vs invalidity

invalid and invalidity both are nouns.

Word	Noun	Adjective	Verb	Adverb
invalid	Yes	Yes	Yes	No
invalidity	Yes	No	No	No

invalid (noun)	invalidity (noun)
someone who is incapacitated by a chronic illness or injury	illogicality as a consequence of having a conclusion that does not follow from the premisses

invalid (adjective)	invalidity (adjective)
having no cogency or legal force
no longer valid

invalid (verb)	invalidity (verb)
injure permanently
force to retire, remove from active duty, as of firemen