grass on (one)(redirected from grass on)
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?
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.