The Collaborative International Dictionary of English v.0.48:

Lavatory \Lav"a*to*ry\, n.; pl. Lavatories. [L. lavatorium:
   cf. lavatoire. See Lave to wash, and cf. Laver.]
   1. A place for washing.
      [1913 Webster]

   2. A basin or other vessel for washing in.
      [1913 Webster]

   3. A wash or lotion for a diseased part.
      [1913 Webster]

   4. A place where gold is obtained by washing.
      [1913 Webster]

   5. A room containing one or more sinks for washing, as well
      as one or more toilet fixtures; also called bathroom,
      toilet, and sometimes commode. Commode and toilet may
      refer to a room with only a toilet fixture, but without a
      sink.

   Syn: toilet, lavatory, can, facility, john, privy, bathroom.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

bathroom
    n 1: a room (as in a residence) containing a bathtub or shower
         and usually a washbasin and toilet [syn: bathroom,
         bath]
    2: a room or building equipped with one or more toilets [syn:
       toilet, lavatory, lav, can, john, privy,
       bathroom]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "bathroom":
   WC, backhouse, bagnio, balneae, balneum, basement, bath, bathhouse,
   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, washroom, water closet, watering place