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rat (one) out
To inform an authority figure of one's bad or illegal behavior. I can't believe you ratted me out like that to Mom and Dad—I'm never telling you anything ever again! The criminal ratted out his accomplices to avoid jail time.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
Sl. to quit; to fink out (on someone or something). It's too late to rat out. He tried to rat out at the last minute.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
To expose or reveal incriminating or embarrassing information about someone: The newspapers ratted out the people who were involved with the scam.
The American Heritage® Dictionary of Phrasal Verbs. Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
in. to quit; to fink out (on someone/something). He tried to rat out at the last minute.
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.