grass on (one)

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grass on (one)

slang To inform against a criminal or wrongdoer to a figure of authority. Primarily heard in UK. I'm afraid the Mafia will make a hit on me since I grassed on them to the police about their money-laundering operation. Why would you grass on me to the teacher like that?
See also: grass, on
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
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