Definition of rat noun from the Oxford Advanced Learner's Dictionary

     

    rat

     noun
    noun
    BrE BrE//ræt//
     
    ; NAmE NAmE//ræt//
     
    Wild mammals
     
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  1. 1a small animal with a long tail, that looks like a large mouse, usually considered a pest (= an animal which is disliked because it destroys food or spreads disease) rat poison The police are all over town. He’s caught, like a rat in a trap. compare rug rat See related entries: Wild mammals
  2. 2(informal, disapproving) an unpleasant person, especially one who is not loyal or who tricks somebody You mean he just walked out on her after fifteen years? What a rat!
  3. Word Origin Old English ræt, probably of Romance origin; reinforced in Middle English by Old French rat. The verb dates from the early 19th cent.Extra examples Rats had gnawed through the wires. The dog was a useful rat catcher in the warehouse. a rat-infested cellarIdioms
    (like rats) deserting/leaving a sinking ship
     
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    (humorous, disapproving) used to talk about people who leave an organization, a company, etc. that is having difficulties, without caring about the people who are left
    (informal) to suspect that something is wrong about a situation
See the Oxford Advanced American Dictionary entry: rat