WordNet (r) 3.0 (2006):

operating room
    n 1: a room in a hospital equipped for the performance of
         surgical operations; "great care is taken to keep the
         operating rooms aseptic" [syn: operating room, OR,
         operating theater, operating theatre, surgery]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "operating room":
   X ray, blood bank, charity ward, clinic, consultation room,
   delivery room, dispensary, emergency, examining room, fever ward,
   hospital room, intensive care, isolation, labor room, laboratory,
   maternity ward, nursery, pharmacy, prison ward, private room,
   recovery room, semi-private room, surgery, therapy, treatment room,
   ward