am·phi·the·a·ter / ˈamfəˌ[unvoicedth]ēətər/ • n. (esp. in Greek and Roman architecture) a round building, typically unroofed, with a central space for the presentation of dramatic or sporting events. Tiers of seats surround the central space. ∎  a sloping, semicircular seating gallery: a lecture in the amphitheater of the hospital. ∎  a large circular hollow in rocks or hills.

amphitheatre Flat-topped, steep-walled, depression, shaped like a horseshoe and resembling an ancient Greek theatre. It may be the result of glacial erosion, forming a cirque, or the collapse of a volcano. In the case of Mount St Helens, the catastrophic collapse of the summit and northern slopes of the cone and the subsequent pyroclastic flow eruption on 18 May 1980 created a north-facing amphitheatre enclosing a small active vent, later occupied by a small dacite dome.

amphitheatre In ancient Rome and the Roman Empire, a large circular or oval building with the performance space surrounded by tiered seating. It was used as a theatre for gladiatorial contests, wild-animal shows and similar events. Many ruined amphitheatres remain; the best-known being the Colosseum in Rome. The term is now used generically to refer to any open, banked arena.

amphitheatre A flat-topped, steep-walled, depression that is shaped like a horseshoe and resembles an ancient Greek theatre. It may be the result of glacial erosion, forming a cirque, or the collapse of a volcano. In the case of Mount St Helens, Washington, the catastrophic collapse of the summit and northern slopes of the cone and the subsequent pyroclastic flow eruption on 18May1980 created a north-facing amphitheatre enclosing a small active vent, later occupied by a small dacite dome.

amphitheatre.
1. Roman building-type resembling two theatres joined together to form an arena, elliptical on plan (viz. the Colosseum in Rome).

2. Bowl-like garden feature, planted or not, sometimes used for open-air performances, with tiers.