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]

The Collaborative International Dictionary of English v.0.48:

Water viper \Wa"ter vi"per\ (Zool.)
   See Water moccasin.
   [1913 Webster]