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. maniacal adj. maniacally adv.
[ LL maniacus f. late Gk maniakos (as MANIA) ]