An Etymological Dictionary of the German Language/Ratte
Ratte, f., from the equiv. MidHG. ratte, rate, f., rat, rate, m., OHG. rato, m., ratta, f., ‘rat’ (in MidHG. there also appears another variant ratz, ratze, m., whence Bav. and Swiss Ratze). It corresponds to OLG. ratta, f., Du. rat, rot, m., AS. rœtt (?), E. rat, Dan. rotte. Besides these are found the Rom. words Fr. rat, Ital. ratto, and also Gael. radan. The origin of all these cognates is unknown. The Rom. class has been derived from Lat. raptus, rapidus; in that case Ital. ratto, ‘quick, nimble,’ would be the primary meaning. The phonetic relations of the Teut. words are not sufficiently clear to pronounce a decided opinion (comp. Katze).