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 waysynonymmadmanHe was driving like a maniac.2a person who has an extremely strong desire or enthusiasm for something, to an extent that other people think is not normalsynonymfanatic3(psychology)a person suffering from maniaa homicidal maniacmaniacadjective[only before noun]a maniac driver/fan/killer