The Collaborative International Dictionary
Psychopathist
Psychopathy \Psy*chop"a*thy\, n. [Psycho- + Gr. ?, ?.] (Med.) Mental disease. See Psychosis, 2. -- Psy`cho*path"ic, a. -- Psy*chop"a*thist, n.
Wiktionary
psychopathist
n. (context medicine dated English) One who studies mental illness.