Other forms: rating, rated, rats
A rat is a bigger cousin of the mouse, common in cities. Brown rats, a rat in the drain, rat catcher.
The brown rat is the one in British cities and it is a formidable animal — it swims, climbs, gnaws through lead and breeds fast. The claim that you are never more than six feet from a rat is untrue and refuses to die. Figuratively, a rat is somebody who betrays, and to rat on somebody is to inform. Note rat race; smell a rat; and rats as an exclamation.
1nounratA long-tailed rodent larger than a mouse.
“A brown rat weighs about three hundred grams.”
2verbinformTo inform on somebody.
“He ratted on his friends to the police to get a shorter sentence.”
Too few real examples of this word to estimate which sense is commonest.
rat is a rodent.
Old English raet is of uncertain origin, shared across the Germanic and Romance languages, which suggests it spread with the animal itself rather than being inherited.
Proto-Indo-European
*Hreh₃d- — to gnaw, scrape, scratch
Proto-Germanic
*rattaz
Proto-West Germanic
*ratt
Old English
ræt
Middle English
raat
English, today
rat
Built from
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. 2 Cognate with frr root (“rat”), stq Rotte (“rat”), West Frisian rôt (“rat”), Dutch rat, rot (“rat”), German Ratte (“rat”), lb Rat (“rat”), wym rot, rott (“rat”), Yiddish ראַץ (“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 (“to scrape, scratch; to cut path, pave; to lead river into a channel; to bestow, convey”).
Etymology from Wiktionary, CC BY-SA