From Middle English raat, rat, ratt, ratte, rotte, from Old English ræt, rætt, from Proto-West Germanic *ratt, from Proto-Germanic *rattaz, *rattō (“rat”), of uncertain origin, possibly from Proto-Indo-European *Hreh₃d- (“to gnaw, scrape, scratch”). However, the rat may have been unknown in Northern Europe in antiquity, and the Proto-Germanic word may have referred to a different animal; see *rattaz for more. Attestation of this family of words begins in the 12th century. Cognates Cognate with North Frisian root (“rat”), Saterland Frisian Rotte (“rat”), West Frisian rôt (“rat”), Dutch rat, rot (“rat”), German Ratte (“rat”), Luxembourgish Rat (“rat”), Vilamovian rot, rott (“rat”), Yiddish ראַץ (rats, “rat”), Danish and Norwegian Bokmål rotte (“rat”), Faroese and Icelandic rotta (“rat”), Norwegian Nynorsk rotta, rotte, røtte (“rat”), Swedish råtta (“rat”), Latin rattus, ratus (“rat”) (whence Asturian ratu (“mouse”), Catalan rata (“rat”), French rat (“rat”), Italian ratto (“rat”), Portuguese rato (“rat”), Spanish rata (“rat”), rato (“male rat”)); also Latin rōdō (“to bite, gnaw, nibble; to backbite, disparage, slander”), Sanskrit रदति (radati, “to scrape, scratch; to cut path, pave; to lead river into a channel; to bestow, convey”). Some of the Germanic cognates show considerable consonant variation, e.g. Middle Low German ratte, radde; Middle High German rate, ratte, ratze. The irregularity may be symptomatic of a late dispersal of the word, although Kroonen accounts for it with a Proto-Germanic stem *raþō nom., *ruttaz gen., showing both ablaut and a Kluge's law alternation, with the variation arising from varying remodellings in the descendants. Kroonen states that this requires a Proto-Indo-European etymon in final *t and is incompatible with the usual derivation from Proto-Indo-European *Hreh₃d- (“to scrape, scratch, gnaw”).

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