rat

Universal Words noun, verb noun 1 a 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. 2 (informal, disapproving) an unpleasant person, especially one who is not loyal or tricks sb: You mean he just walked out on her after fifteen years? What a rat! IDIOMS see SINKv., SMELLv. verb (-tt-) PHRASALVERBS rat on sb (informal) to tell sb in authority about sth wrong that sb else has done: Where I come from, you don't rat on your friends. rat on sth (BrE, informal) to not do sth that you have agreed or promised to do: The government is accused of ratting on its promises to the unemployed.