inform on

inform on (third-person singular simple present informs on, present participle informing on, simple past and past participle informed on)

1. To tell on someone; to act as an informant against.
   • 2013 May 24, Emily Parker, “Bulgakov's Ghost”, in The New York Times‎, archived from the original on 2022-05-12:

     In 1983, one of his friends informed on him for reading a forbidden book, and he lost his teaching job.

• finger, grass up, snitch; See also Thesaurus:rat out