The Collaborative International Dictionary of English v.0.48:

moccasin \moc"ca*sin\, n. [An Indian word. Algonquin makisin.]
   [Sometimes written moccason.]
   1. A shoe made of deerskin, or other soft leather, the sole
      and upper part being one piece. It is the customary shoe
      worn by the American Indians.
      [1913 Webster]

   2. (Zool.) A poisonous snake of the Southern United States.
      The water moccasin (Ancistrodon piscivorus syn.
      Agkistrodon piscivorus, also called cottonmouth and
      cottonmouth water moccasin) is usually found in or near
      water. Above, it is olive brown, barred with black;
      beneath, it is brownish yellow, mottled with darker. The
      upland moccasin is Ancistrodon atrofuscus. They resemble
      rattlesnakes, but are without rattles.
      [1913 Webster]

   Moccasin flower (Bot.), a species of lady's slipper
      (Cypripedium acaule) found in North America. The lower
      petal is two inches long, and forms a rose-colored
      moccasin-shaped pouch. It grows in rich woods under
      coniferous trees.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Water moccasin \Wa"ter moc"ca*sin\ (Zool.)
   A venomous North American snake (Ancistrodon piscivorus)
   allied to the rattlesnake but destitute of a rattle. It lives
   in or about pools and ponds, and feeds largely of fishes.
   Called also water snake, water adder, water viper.
   [1913 Webster]