the race-migrations" and the word passing thence to the Romanic languages. American Heritage and Tucker connect O.E. ræt to L. rodere and thus PIE *red- "to scrape, scratch, gnaw," source of rodent
(q.v.). Klein says there is no connection and suggests a possible cognate in Gk. rhine "file, rasp." Weekley connects them with a question mark and Barnhart writes, "the relationship to each other of the Germanic, Romance, and Celtic words for rat is uncertain." OED says "probable" the rat word spread from Germanic to Romance, but takes no position on ultimate origin. M.E. common form was ratton, from augmented O.Fr. form raton. Sense of "one who abandons his associates" (1629) is from belief that rats leave a ship about to sink or a house about to fall and led to meaning "traitor, informant" (1902; verb 1910). Interjection rats is Amer.Eng., 1886. To smell a rat is c.1550. Rat-race "competitive struggle" is 1939. Ratsbane (1523) is arsenic. Rat fink is teen slang from 1963. Rathole in fig. sense of "nasty, messy place" first attested 1812. _____-rat, "person who frequents _____" (in earliest ref. dock-rat) is from 1864. Rat-pack "juvenile gang" is from 1951.