n. & adj.
--n.
1. colloq. a person exhibiting extreme symptoms of wild behaviour etc.; a madman.
2 colloq. an obsessive enthusiast.
3 Psychol. archaic a person suffering from mania.
--adj. of or behaving like a maniac.
Derivatives:
maniacal adj. maniacally adv.
Etymology: LL maniacus f. late Gk maniakos (as MANIA)