any of a very large order (Rodentia) of gnawing mammals, including rats, mice, squirrels, and beavers, characterized by constantly growing incisors adapted for gnawing or nibbling; esp., in popular usage, a rat or mouse
See rodent in American Heritage Dictionary 4
(rōdˈnt)
noun
Any of various mammals of the order Rodentia, such as a mouse, rat, squirrel, or beaver, characterized by large incisors adapted for gnawing or nibbling.