psych(o)-

The mind; psychology.

Greek psukhē, breath, soul, mind.

Psychology is the scientific study of the human mind and its functions, while psychiatry studies and treats mental illness, emotional disturbance, and abnormal behaviour; a psychopath is a person suffering from chronic mental disorder with abnormal or violent social behaviour; psychotherapy is the treatment of mental disorder by psychological rather than medical means; a psychedelic drug (Greek delos, clear, manifest) is one, especially LSD, that produces hallucinations and apparent expansion of consciousness.

Several terms relate to cross-disciplinary subjects involving psychology or perception: psychoacoustics is the branch of psychology concerned with the perception of sound and its physiological effects; psychobiology deals with the biological basis of behaviour and mental phenomena; psychohistory interprets historical events with the aid of psychological theory; psycholinguistics studies the relationships between linguistic behaviour and psychological processes.