How is “tip off” used?

In Slacker (1990), one line is: “Yeah, yeah. It was the tip-off for Oswald, you know?”

Which movie is “tip off” from?

The clip at the top of this page is from Slacker (1990).

Yeah, yeah. It was the tip-off for Oswald, you know?

8 作品で登場 · 1 本目

句動詞

to warn sb about sth that is going to happen, especially sth illegal

くだけた · 8 本の映画に登場

tip sb off (about sth)
to warn sb about sth that is going to happen, especially sth illegal
Three men were arrested after police were tipped off about the raid.

定義：Oxford Advanced Learner's Dictionary 第 9 版