amphitheater (n.)youdaoicibaDictYouDict[amphitheater 词源字典]
late 14c., from Latin amphitheatrum, from Greek amphitheatron "double theater, amphitheater," neuter of amphitheatros "with spectators all around," from amphi- "on both sides" (see amphi-) + theatron "theater" (see theater). Classical theaters were semi-circles, thus two together made an amphi-theater.[amphitheater etymology, amphitheater origin, 英语词源]