inform on
US /ɪnˈfɔːrm ɑːn/
UK /ɪnˈfɔːrm ɑːn/

1.
告发, 举报
to give information to the police or other authority about someone's illegal or wrong activities
:
•
He decided to inform on his accomplices to get a lighter sentence.
他决定告发他的同伙以获得减刑。
•
Are you going to inform on your friend for cheating?
你打算告发你朋友作弊吗?