The Collaborative International Dictionary of English v.0.48:

Catamaran \Cat`a*ma*ran"\, n. [The native East Indian name.]
   1. A kind of raft or float, consisting of two or more logs or
      pieces of wood lashed together, and moved by paddles or
      sail; -- used as a surf boat and for other purposes on the
      coasts of the East and West Indies and South America.
      Modified forms are much used in the lumber regions of
      North America, and at life-saving stations.
      [1913 Webster]

   2. Any vessel with twin hulls, whether propelled by sails or
      by steam; esp., one of a class of double-hulled pleasure
      boats remarkable for speed.
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   3. A kind of fire raft or torpedo bat.
      [1913 Webster]

            The incendiary rafts prepared by Sir Sidney Smith
            for destroying the French flotilla at Boulogne,
            1804, were called catamarans.         --Knight.
      [1913 Webster]

   4. A quarrelsome woman; a scold. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

catamaran
    n 1: a sailboat with two parallel hulls held together by single
         deck