From Middle High German ratte, from Old High German ratta. There is still some uncertainty about the origin of the word and that of the animal itself, which was unknown to Europe in antiquity. Older etymological sources explain the Germanic words as borrowings from Romance. It is now widely accepted that this is not the case. The further etymology is unsettled. The word may go back to an unknown substrate language, or be formed from a Proto-Indo-European root meaning „to gnaw“ (compare Latin rōdere). The consonantism ratta in Old High German (instead of *razza), along with other hints, makes it likely that the former is borrowed from Old Saxon ratta. The dialectal German variant Ratz is probably an expressive derivative, though it could be an Old High German adaptation of the Old Saxon form. See English rat for more. Compare also Dutch rat, Swedish råtta, French rat.
- Ratte in Duden online