Which of the following is a term for a medical specialist?

The suffix "-ologist" is used to denote a medical specialist who studies or has expertise in a particular area of medicine. For example, a cardiologist is a specialist in heart-related issues, while a dermatologist focuses on conditions of the skin. This term indicates a focus on diagnosis and treatment within a specific field, which is essential for understanding various medical professions and specialties.

The other terms provided have different meanings: "-opathy" refers to a disease or disorder, often implying a specific pathology, as seen in terms like "neuropathy." "-genesis" signifies the origin or creation of something, often used in contexts such as "pathogenesis," which discusses the development of disease. Lastly, "-rrhea" relates to flow or discharge, as in "diarrhea," which refers to a condition characterized by frequent, watery bowel movements. Each of these terms serves a distinct function within medical terminology, but none pertain to a medical specialist in the same way that "-ologist" does.