noun

1. a round or oval building with an open space (arena) surrounded by rising rows of seats
2. a scene of conflict, competition, etc.; arena
3. a sloping gallery in a theater
4. a lecture hall with a sloping gallery, esp. one for observing surgical procedures in a medical school or hospital
5. a level place surrounded by rising ground

Etymology: L amphitheatrum < Gr amphitheatron: see amphi- & theater