ma·ni·ac 
(mānē-ăk′)
(mānē-ăk′)n.
1. A psychotic or otherwise mentally ill person who exhibits violent or bizarre behavior. Not used in psychiatric diagnosis.
2. A person who has an excessive enthusiasm or desire for something: a sports maniac.
3. A person who acts in a wildly irresponsible way: maniacs on the highway.
adj.
Variant of maniacal.
[From Late Latin maniacus, maniacal, from Greek maniakos, from maniā, madness; see men-1 in the Appendix of Indo-European roots.]