The Collaborative International Dictionary of English v.0.48:

Steamer \Steam"er\ (-[~e]r), n.
   1. A vessel propelled by steam; a steamship or steamboat.
      [1913 Webster]

   2. A steam fire engine. See under Steam.
      [1913 Webster]

   3. A road locomotive for use on common roads, as in
      agricultural operations.
      [1913 Webster]

   4. A vessel in which articles are subjected to the action of
      steam, as in washing, in cookery, and in various processes
      of manufacture.
      [1913 Webster]

   5. (Zool.) The steamer duck.
      [1913 Webster]

   Steamer duck (Zool.), a sea duck (Tachyeres cinereus),
      native of Patagonia and Terra del Fuego, which swims and
      dives with great agility, but which, when full grown, is
      incapable of flight, owing to its very small wings. Called
      also loggerhead, race horse, and side-wheel duck.
      [1913 Webster]

WordNet (r) 3.0 (2006):

steamer
    n 1: a clam that is usually steamed in the shell [syn: soft-
         shell clam, steamer, steamer clam, long-neck clam]
    2: a cooking utensil that can be used to cook food by steaming
       it
    3: a ship powered by one or more steam engines [syn: steamer,
       steamship]
    4: an edible clam with thin oval-shaped shell found in coastal
       regions of the United States and Europe [syn: soft-shell
       clam, steamer, steamer clam, long-neck clam, Mya
       arenaria]
    v 1: travel by means of steam power; "The ship steamed off into
         the Pacific" [syn: steamer, steam]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "steamer":
   Dungeness crab, Japanese crab, blue point, clam, coquillage, crab,
   crawdad, crawfish, crayfish, langouste, limpet, littleneck clam,
   lobster, mussel, oyster, periwinkle, prawn, quahog, scallop,
   shellfish, shrimp, snail, soft-shell crab, steamboat, steamship,
   whelk