inform on

inform on (one)

To share or reveal compromising or incriminating information about one, especially to the police or other figures of authority. If you inform on him to the cops, he'll definitely send some of his goons out after you. Yeah, I know about your shady deals, but I didn't inform on you, I swear!
See also: inform, on
Farlex Dictionary of Idioms.

inform someone on someone

to tattle (on someone) (to someone). I will inform the teacher on you! Billy informed his mother on Bobby.
See also: inform, on

inform on someone

to tell the authorities about someone; to tattle on someone. I am going to have to inform on you. Liz informed on Ken to their mother.
See also: inform, on
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

inform on

or inform against
v.
To disclose confidential or incriminating evidence about someone to an authority: The FBI agent informed on the drug dealers. You can't force me to inform against my own family.
See also: inform, on
The American Heritage® Dictionary of Phrasal Verbs.
See also:
  • inform on (one)
  • inform against (one)
  • mouth on
  • mouth on (one)
  • dob in
  • have (something) on (one)
  • have on one
  • have something on somebody
  • grasser
  • sung