Rat
Old English ræt, probably of Romance origin; reinforced in Middle English by Old French rat . The verb dates from the early 19th century.
wiktionary
From Middle English ratte, rat, rotte, from Old English rætt, from Proto-Germanic *rattaz, *rattō (compare West Frisian rôt, Dutch rat), of uncertain origin, possibly from Proto-Indo-European *reh₁d-(“to scrape, scratch, gnaw”). 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. [1] Attestation of this family of words begins in the 12th century.[citation needed]
Some of the Germanic cognates show considerable consonant variation, e.g. Middle Low German ratte, radde; Middle High German rate, ratte, ratze. [1] 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., [1] 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 *reh₁d-(“to scrape, scratch, gnaw”). [1]
From Middle English ratten, further etymology unknown. Compare Middle High German ratzen(“to scratch; rasp; tear”). Could be related to write. See also rit.
rat (plural rats)
etymonline
rat (n.)
"a rodent of some of the larger species of the genus Mus," late Old English ræt "rat," a word of uncertain origin. Similar words are found in Celtic (Gaelic radan), Romanic (Medieval Latin ratus, Italian ratto, Spanish rata, Old French rat) and Germanic (Old Saxon ratta; Middle Dutch ratte, Dutch rat; German Ratte, dialectal Ratz; Swedish råtta, Danish rotte) languages, but their connection to one another and the ultimate source of the word are unknown. In its range and uncertain origin, it is much like cat.
Perhaps from Vulgar Latin *rattus, but Weekley thinks this is of Germanic origin, "the animal having come from the East with the race-migrations" and the word passing thence to the Romanic languages. American Heritage and Tucker connect Old English ræt to Latin rodere and thus to PIE root *red- "to scrape, scratch, gnaw," source of rodent (q.v.). Klein says there is no such connection and suggests a possible cognate in Greek rhine "file, rasp." Weekley connects the English noun and the Latin verb with a question mark and OED says it is "probable" that the rat word spread from Germanic to Romanic, but takes no position on further etymology. The common Middle English form was ratton, from augmented Old French form raton. Applied to rat-like species on other continents from 1580s.
The distinction between rat and mouse, in the application of the names to animals everywhere parasitic with man, is obvious and familiar. But these are simply larger and smaller species of the same genus, very closely related zoologically, and in the application of the two names to the many other species of the same genus all distinction between them is lost. [Century Dictionary]
Applied since 12c. (in surnames) to persons held to resemble rats or share some characteristic or quality with them. Specific sense of "one who abandons his associates for personal advantage" (1620s) is from the belief that rats leave a ship about to sink or a house about to fall, and this led to the meaning "traitor, informant" (1902).
To smell a rat "to be put on the watch by suspicion as the cat by the scent of a rat; to suspect danger" [Johnson] is from 1540s. _____-rat, "person who frequents _____" (in earliest reference dock-rat) is from 1864.
RATS. Of these there are the following kinds: a black rat and a grey rat, a py-rat and a cu-rat. ["Dictionary of the Vulgar Tongue," Grose, 1788]
rat (v.)
1812, "to desert one's party, go over from a losing cause;" 1847 as "to work for less than current wages, refuse to join a labor strike;" 1864 as "to catch or kill rats;" 1910 as "to peach on, inform on, behave dishonestly toward;" from rat (n.). All but the third are extended from the proverbial belief that rats leave a ship about to sink or a house about to fall. Related: Ratted; ratting.
