Also found in: Legal.
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.
inform someone on someone
to tattle (on someone) (to someone). I will inform the teacher on you! Billy informed his mother on Bobby.
inform onor inform against
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.