WordNet (r) 3.0 (2006):

water closet
    n 1: a toilet in Britain [syn: water closet, closet, W.C.,
         loo]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "water closet":
   WC, backhouse, basement, bathroom, bedpan, can, chamber,
   chamber pot, chemical closet, chemical toilet, closet,
   comfort station, commode, convenience, crapper, earth closet, head,
   jerry, john, johnny, johnny house, jordan, latrine, lavatory, loo,
   necessary, outhouse, piss pot, potty, potty-chair, powder room,
   privy, rest room, stool, throne, thunder mug, toilet, toilet room,
   urinal, washroom