The black rat, Rattus rattus.

The brown rat.

A brown rat. / (slang) A neglected boy who lives around the wharfs. / (slang) A man who hangs around a wharf in the hope of finding temporary work there.

The brown rat.

Alternative spelling of pack rat

Any of several small North American rodents, of the genus Neotoma, that have bushy tails. / One who collects or hoards, especially unnecessary things.

(US) Any of various aquatic or semi-aquatic rodents from Florida and southern Georgia, especially Neofiber alleni; the muskrat. / (Australia) A water mouse, especially, the rakali, Hydromys chrysogaster.

(literally) A rat that lives on or along a river. / (chiefly derogatory) A lower-class person living on or along a river.

Alternative spelling of mole-rat.

(slang) A class ring bearing the image of a beaver, worn by graduates of MIT.