An Etymological Dictionary of the German Language/Annotated/Ratte
Ratte, feminine, from the equivalent Middle High German ratte, rate, feminine, rat, rate, masculine, Old High German rato, masculine, ratta, feminine, ‘rat’ (in Middle High German there also appears another variant ratz, ratze, masculine, whence Bavarian and Swiss Ratze). It corresponds to Old Low German ratta, feminine, Dutch rat, rot, masculine, Anglo-Saxon rœtt (?), English rat, Danish rotte. Besides these are found the Romance words French rat, Italian ratto, and also Gaelic radan. The origin of all these cognates is unknown. The Romance class has been derived from Latin raptus, rapidus; in that case Italian ratto, ‘quick, nimble,’ would be the primary meaning. The phonetic relations of the Teutonic words are not sufficiently clear to pronounce a decided opinion (compare Katze).