It is derived from the Greek word "iatros" meaning "physician" or "healer".
Here are some examples:
* Psychiatrist: A specialist in the treatment of mental disorders.
* Pediatrician: A specialist in the treatment of children.
* Geriatrician: A specialist in the treatment of elderly people.
* Dermatologist: A specialist in the treatment of skin diseases.
* Cardiologist: A specialist in the treatment of heart diseases.
Essentially, whenever you see "-iatrist" at the end of a word, it tells you that the person is a doctor who specializes in that particular field.