definition of maniac
maniac noun [C] (MENTALLY ILL). âº a âperson who âbehaves in an uncontrolled way, not âworrying about ârisks or âdanger: Some maniac was ârunning down the âstreet âwaving a âmassive âmetal âbar.informal I won't get in the âcar with Richard-he âdrives like a maniac! Idioms.