V on n
II.11 The 'inform' group
These verbs are concerned with telling people in authority that someone has done something wrong. The prepositional phrase indicates who that person is. The implication is usually that the person referred to by the Subject betrays the other person by giving this information.
grass inform rat snitch tell
This is a tense thriller about a diamond heist that goes badly wrong because someone has grassed on the thieves.
They had to attend indoctrination sessions at which they were urged to inform on suspected 'separatists'.