loony vs loon

loony and loon both are nouns.

Word	Noun	Adjective	Verb	Adverb
loony	Yes	Yes	No	No
loon	Yes	No	No	No

loony (noun)	loon (noun)
someone deranged and possibly dangerous	large somewhat primitive fish-eating diving bird of the Northern Hemisphere having webbed feet placed far back; related to the grebes
	a worthless lazy fellow
	a person with confused ideas; incapable of serious thought

loony (adjective)	loon (adjective)
informal or slang terms for mentally irregular