operating theater operating theater /ˈɑːpəreɪtɪŋ ˈθiːətər/

noun

1. [American] A room in a hospital equipped for the performance of surgical operations  ( operating room [ N. American] , operating theater [American] , operating theatre , OR [ N. American] , surgery )
   a room in a hospital equipped for the performance of surgical operations
    Great care is taken to keep the operating rooms aseptic
   great care is taken to keep the operating rooms aseptic