maniac vs crazy

maniac and crazy both are nouns.

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

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

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

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

maniac (adjective)	crazy (adjective)
wildly disordered	intensely enthusiastic about or preoccupied with
	possessed by inordinate excitement
	foolish; totally unsound
	affected with madness or insanity
	bizarre or fantastic