noun
1. : a rodent that frequents water: as
a. : a vole of the genus Arvicola ; especially : a common large British vole ( A. amphibius )
b. : brown rat ; broadly : an amphibious rodent of the genus Rattus
c. : muskrat ; especially : round-tailed muskrat
d. : any of various Australasian rodents of Hydromys or a related genus : beaver rat
e. : any of several moderate-sized southern African rats (genus Dasymys ) with long silky fur and scaly tails that commonly inhabit reedbeds
2. : a waterfront loafer or petty thief