1. any of various rodents having aquatic habits.
2. the muskrat, Ondatra zibethica.
3. (in Australia and New Guinea) any of the aquatic rats of the subfamily Hydromyinae, esp. of the genus Hydromys.
4. Slang.a vagrant or thief who frequents a waterfront.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.