maniac vs loony

maniac and loony both are nouns.

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

As nouns, loony is a hyponym of maniac; that is, loony is a word with a more specific, narrower meaning than maniac:

Other hyponyms of maniac include crazy, looney, nutcase, weirdo, bedlamite, pyromaniac, madwoman, madman.

maniac (noun)	loony (noun)
an insane person	someone deranged and possibly dangerous
a person who has an obsession with or excessive enthusiasm for something

maniac (adjective)	loony (adjective)
wildly disordered	informal or slang terms for mentally irregular