Neurologist, psychiatrist, alienist, psychopathologist, psychotherapist, psychoanalyst are comparable though not synonymous terms that denote a specialist in mental disorders.
A neurologist is a physician skilled in the diagnosis and treatment of diseases of the nervous system, that is, of diseases (as epilepsy or locomotor ataxia) that involve structural or functional disorder of nervous tissue.
Psychiatrist, alienist, psychopathologist all designate a physician who devotes himself to the diagnosis and treatment of diseases affecting the mind or emotions and especially, as distinguished from neurologist, of disorders (as neurasthenia, hysteria, and paranoia) not demonstrably of physical origin.
Psychiatrist is the general term, applicable to any such physician, while alienist is the preferred term in medical jurisprudence and may especially suggest skill in detection of mental derangements or of insanity, and psychopathologist may specifically apply to a physician specializing in emotional disorders and dealing largely with the dynamic factors (as defects of personality or unfavorable environment) underlying such disorders.
A psychotherapist may be either a physician or a layman (as a psychologist, social worker, or clergyman) who treats mental or emotional disorder or maladjustment by psychological means and especially those involving verbal communication.
A psychoanalyst is a psychotherapist and usually a physician (nonmedical psychoanalysts being often distinguished as lay analysts ) who employs a form of psychotherapy, especially in the treatment of psychoneuroses, that is designed to bring unconscious and preconscious material into consciousness and involves largely the analysis of resistance and the establishment and analysis of a transference neurosis.