-ist

(Greek > Latin: a suffix; one who believes in; one who is engaged in; someone who does something)

pseudologist
pseudomantist
psilanthropist (s) (noun), psilanthropists (pl)
Someone who believes that Jesus was not divine but merely a man: Psilanthropists generally deny both the virgin birth of Jesus and his deity or holiness.
psychiatrist
A physician who specializes in the study, treatment, and prevention of mental disorders.
psychologist
1. Someone who is trained in methods of psychological analysis, therapy, and research.
2. A specialist in psychology licensed to practice professional psychology (e.g., clinical psychologist), or qualified to teach psychology as a scholarly discipline (academic psychologist), or whose scientific specialty is a subfield of psychology (research psychologist).
psychopathist
An obsolete term for a psychiatrist.
psychopathologist (s) (noun), psychopathologists (pl)
Someone who specializes in mental and behavioural disorders: Mr. Smart, Mary's father, was a psychopathologist who studied and did research of the origins, the processes of development, and the identification of mental disorders, including possible cures and treatments.
psychophysiologist
Someone who studies psychophysiology.
psychosomaticist
A specialist in psychosomatic (mind and body) disorders.
psychotherapist
A person, usually a psychiatrist or clinical psychologist, professionally trained and engaged in psychotherapy. Currently, the term is also applied to social workers, nurses, and others whose state licensing practice acts include psychotherapy.
pterylologist
ptochologist (s) (noun), ptochologists (pl)
Those who specialize in the study of people who are extremely poor: Ptochologists are finding an increase in the number of people who have been affected by poverty and are existing in shelters (temporary housing for homeless or displaced persons) or on the streets with few or no possessions.
publicist
Someone who arranges publicity for a person or organization by giving information to reporters and broadcasters and arranging public meetings and special events.
puellaphilist (s) (noun), puellaphilists (pl)
In psychiatry, one who has a special love for young girls: In one of her classes at medical school, Susan learned that a puellaphilist was a person who worshiped female children and might even have a sexual desires for them.
puericulturist
One who raises and trains children.