invalid vs valid

invalid is a noun but valid is not a noun.

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

invalid (noun)	valid (noun)
someone who is incapacitated by a chronic illness or injury

invalid (adjective)	valid (adjective)
having no cogency or legal force	well grounded in logic or truth or having legal force
no longer valid	still legally acceptable

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