The Collaborative International Dictionary of English v.0.48:

Dressing \Dress"ing\, n.
   1. Dress; raiment; especially, ornamental habiliment or
      attire. --B. Jonson.
      [1913 Webster]

   2. (Surg.) An application (a remedy, bandage, etc.) to cover
      a sore or wound. --Wiseman.
      [1913 Webster]

   3. Manure or compost over land. When it remains on the
      surface, it is called a top-dressing.
      [1913 Webster]

   4. (Cookery)
      (a) A preparation, such as a sauce, to flavor food for
          eating; a condiment; as, a dressing for salad.
      (b) The stuffing of fowls, pigs, etc.; forcemeat.
          [1913 Webster]

   5. Gum, starch, and the like, used in stiffening or finishing
      silk, linen, and other fabrics.
      [1913 Webster]

   6. An ornamental finish, as a molding around doors, windows,
      or on a ceiling, etc.
      [1913 Webster]

   7. Castigation; scolding; -- often with down. [Colloq.]
      [1913 Webster]

   Dressing case, a case of toilet utensils.

   Dressing forceps, a variety of forceps, shaped like a pair
      of scissors, used in dressing wounds.

   Dressing gown, a light gown, such as is used by a person
      while dressing; a study gown.

   Dressing room, an apartment appropriated for making one's
      toilet.

   Top-dressing, manure or compost spread over land and not
      worked into the soil.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dressing room
    n 1: a room in which you can change clothes

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "dressing room":
   L, R, acting area, apron, apron stage, backstage, band shell,
   bandstand, board, bridge, cloakroom, closet, clothes closet,
   coulisse, dock, fitting room, flies, fly floor, fly gallery,
   forestage, greenroom, grid, gridiron, lightboard, linen closet,
   orchestra, orchestra pit, performing area, pit, proscenium,
   proscenium stage, shell, stage, stage left, stage right,
   switchboard, the boards, wardrobe, wings