American English

Definition of rat noun from the Oxford Advanced American Dictionary



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  1. 1a small animal with a long tail, that looks like a large mouse, usually considered a pest (= an animal that 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
  2. 2(informal) (disapproving) an unpleasant person, especially one who is not loyal or who tricks someone You mean he just walked out on her after fifteen years? What a rat!
  3. Idioms
    (like rats) deserting/leaving a sinking ship (humorous) (disapproving)
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    used to talk about people who leave an organization, a company, etc. that is having difficulties, without caring about the people who are left
    smell a rat (informal)
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    to suspect that something is wrong about a situation
See the Oxford Advanced Learner's Dictionary entry: rat