psycho UK /ˈsaɪ̯.kəʊ̯/US /ˈsaɪ̯.koʊ̯/noun 3adjective 1forms 3 noun3 •(slang, offensive) a person with a serious illness of the mindThe loony bin up on the hill is full of psychos. •(slang, offensive) A person who acts in a bizarre or dangerous manner.She complained that he was a psycho for driving at such a high speed in heavy traffic. •(informal) A class, at a college or university, in which psychology is taught.I've got anthro, socio, lunch, and psycho. adjective1 •(informal, offensive) Psychotic, psychopathic, or (broadly) otherwise insane.That psycho jawn had snuck a pistol into the gym while we was practicing and started shooting shit up like she was some kinda hot female action hero. — 2006 formspsychos · more psycho · most psycho