WordNet (r) 3.0 (2006):

washroom
    n 1: a lavatory (particularly a lavatory in a public place)

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "washroom":
   WC, backhouse, bagnio, balneae, balneum, basement, bath, bathhouse,
   bathroom, baths, caldarium, can, closet, comfort station,
   convenience, crapper, earth closet, head, john, johnny,
   johnny house, latrine, lavatory, mikvah, necessary, outhouse,
   powder room, privy, public baths, rest room, sauna, spa,
   steam room, sudarium, sudatorium, sweat room, tepidarium, thermae,
   toilet, toilet room, urinal, water closet, watering place