water snake

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various North American colubrid snakes of the genus Nerodia, living in or frequenting freshwater streams and ponds.
• noun Any of various aquatic or semiaquatic snakes.

from The Century Dictionary.

• noun A snake which frequents the water: variously applied.
• noun Especially—
• noun Any one of the venomous sea-snakes. See Hydrophidæ and sea-serpent, 2, with cuts there or there cited.
• noun The Indian Fordonia unicolor, or any member of the family Homalopsidæ.
• noun A wart-snake; any member of the Acrochordidæ, as species of Acrochordus and Chersydrus. See cut under wart-snake.
• noun The common ringed snake of Europe, Tropidonotus natrix. See cuts under snake and Tropidonotus.
• noun In the United States, one of several harmless aquatic colubrines, as the species of Nerodia (or Tropidonotus) and Regina, as N. sipedon and R. leberis. In the West several species of garter-snakes (Eutænia) are thoroughly aquatic, and would come locally under this name. See water-adder and water-moccasin.

from the GNU version of the Collaborative International Dictionary of English.

• A common North American colubrine snake (Tropidonotus sipedon) which lives chiefly in the water.
• Any species of snakes of the family Homalopsidæ, all of which are aquatic in their habits.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various mostly harmless snakes that live in or near water