Definition: to tell someone that something has happened or is going to happen when other people were trying to keep it a secret.
E.g.1: I heard some girls planning a burglary. I have to tip off the police. If they are tipped off, they will be able to stop it.
E.g.2: A loyal associate tipped the drug dealer off that the police were on their way, so he escaped.
This phrasal verb can be separated. (E.g. 2)