Definify.com
Webster 1913 Edition
Water dog
Wa′ter dogˊ
.1.
(Zool.)
A dog accustomed to the water, or trained to retrieve waterfowl. Retrievers, waters spaniels, and Newfoundland dogs are so trained.
2.
(Zool.)
The menobranchus.
3.
A small floating cloud, supposed to indicate rain.
4.
A sailor, esp. an old sailor; an old salt.
[Colloq.]