1. (noun)rat any of various long-tailed rodents similar to but larger than a mouse
2. (noun)scab, strikebreaker, blackleg, rat someone who works (or provides workers) during a strike
3. (noun)rotter, dirty dog, rat, skunk, stinker, stinkpot, bum, puke, crumb, lowlife, scum bag, so-and-so, git a person who is deemed to be despicable or contemptible "only a rotter would do that"; "kill the rat"; "throw the bum out"; "you cowardly little pukes!"; "the British call a contemptible person a `git'"
4. (noun)informer, betrayer, rat, squealer, blabber one who reveals confidential information in return for money
5. (verb)rat a pad (usually made of hair) worn as part of a woman's coiffure
11. (verb)denounce, tell on, betray, give away, rat, grass, shit, shop, snitch, stag give away information about somebody "He told on his classmate who had cheated on the exam"
Definitions of 'rat'
Webster 1913 Dictionary
1. (noun)rat one of several species of small rodents of the genus Mus and allied genera, larger than mice, that infest houses, stores, and ships, especially the Norway, or brown, rat (M. decumanus), the black rat (M. rattus), and the roof rat (M. Alexandrinus). These were introduced into America from the Old World
3. (noun)rat one who deserts his party or associates; hence, in the trades, one who works for lowerwages than those prescribed by a trades union
4. (verb)rat in English politics, to desert one's party from interested motives; to forsake one's associates for one's own advantage; in the trades, to work for less wages, or on other conditions, than those established by a trades union
Definition of rat 
