Other forms: tipped off; tipping off; tips off
To tip off is to confidentially offer someone a hint or piece of advice. It would be kind to tip off your younger sibling about those pop quizzes the math teacher gives every Friday.
When you offer a tip, especially one based on insider information, you tip someone off. You might tip off a visiting friend about the best pizza place in town, or tip off a store owner that you spotted a shoplifter shoving a sweater in his backpack. Tip off is also used in sports, for the start of a basketball game: "Meet me by 7:00 — the game tips off at 7:30!"