rodent [M19th] The teeth of rodents such as rats and mice grow continuously and must be kept worn down by gnawing, a fact that gives a clue about the origin of the term rodent. The word comes from Latin rodere ‘to gnaw’, which is related to erode [E17th], *corrode, *root, and *rostrum. The original sense of the word is preserved in that unpleasant affliction the rodent ulcer.