A psycho is someone who has serious mental problems and who may act in a violent way without feeling sorry for what they have done. Some psycho picked her up, and killed her. = psychopath. a US horror film (= a film that is intended to make you feel frightened) made by Alfred Hitchcock. Its most famous scene is the one in which the character acted by Janet Leigh is killed with a knife by Norman Bates, played by Anthony Perkins, while she is in the shower (1960). psychos someone who is mentally ill and who may behave in a violent or strange way