Definition of maniac noun from the Oxford Advanced American Dictionary

maniac

noun
/ˈmeɪniˌæk/
 
 
1 (informal) a person who behaves in an extremely dangerous, wild, or stupid way synonym madmanHe was driving like a maniac.2 a person who has an extremely strong desire or enthusiasm for something, to an extent that other people think is not normal synonym fanatic3 (psychology) a person suffering from maniaa homicidal maniac maniac adjective [only before noun]a maniac driver/fan/killer