an animal that looks like a large mouse with a long tail.——朗文当代大辞典

Any rodent of the genus Rattus and related genera of the family Muridae, resembling a large mouse, often with a naked or sparsely haired tail; esp. the cosmopolitan R. norvegicus (more fully brown, common, or Norway rat), and R. rattus (more fully black, ship, house, or roof rat).——牛津当代大辞典  @en