Merriam-Webster Collegiate Dictionary - amphitheater

 noun  Etymology: Latin amphitheatrum, from Greek amphitheatron, from amphi- + theatron theater  Date: 14th century  1. an oval or circular building with rising tiers of seats ranged about an open space and used in ancient Rome especially for contests and spectacles  2.  a. a very large auditorium  b. a room with a gallery from which doctors and students may observe surgical operations  c. a rising gallery in a modern theater  d. a flat or gently sloping area surrounded by abrupt slopes  3. a place of public entertainment (as for games or concerts)  • amphitheatric or amphitheatrical adjective  • amphitheatrically adverb