Any mammal of the worldwide order Rodentia, making up nearly half of all mammal species. Besides ordinary “cheek teeth”, they have a single front pair of incisor teeth in both upper and lower jaw, which continue to grow as they are worn down.
They are often subdivided into three suborders: Sciuromorpha, including primitive rodents, with the squirrels as modern representatives; Caviomorpha, including all the South American rodents, of which the guinea pig is representative; and Myomorpha, rats and mice and their relatives.
Relatively small gnawing animals having a single pair of constantly growing incisor teeth specialized for gnawing; SYN. gnawer, gnawing animal.