From The Collaborative International Dictionary of English v.0.48 :
cottonmouth \cottonmouth\ n.
venomous semiaquatic snake ({Agkistrodon piscivorus) of
swamps in southern U.S.; -- called also water moccasin,
cottonmouth moccasin, and cottonmouth water moccasin. It
grows to a length of about 4 feet. The name refers to the
whiteness of the lips and inside of the mouth.
Syn: water moccasin, cottonmouth moccasin, Agkistrodon
piscivorus.
[WordNet 1.5 +PJC]
From WordNet (r) 3.0 (2006) :
cottonmouth moccasin
n 1: venomous semiaquatic snake of swamps in southern United
States [syn: water moccasin, cottonmouth, cottonmouth
moccasin, Agkistrodon piscivorus]