invalid vs shut-in

invalid and shut-in both are nouns.

Word	Noun	Adjective	Verb	Adverb
invalid	Yes	Yes	Yes	No
shut-in	Yes	Yes	No	No

As nouns, invalid and shut-in are synonyms defined as:

invalid and shut-in: someone who is incapacitated by a chronic illness or injury

invalid (noun)	shut-in (noun)
someone who is incapacitated by a chronic illness or injury	someone who is incapacitated by a chronic illness or injury

invalid (adjective)	shut-in (adjective)
having no cogency or legal force	confined usually by illness
no longer valid	somewhat introverted

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