A tin whistle.

A high-pitched whistle, inaudible to humans, used to train dogs. / (figuratively) That which is understood only by a narrow demographic.

The action of a whistleblower.

(idiomatic) A small train station. / (politics) A brief stop on a campaign tour to make a speech or perform some other type of public electioneering.

(idiomatic) Extremely brief and hurried.

(politics, intransitive) To make a brief stop on a campaign tour to make a speech or perform some other type of public electioneering.

Alternative spelling of wolf whistle

A whistle, of two notes, to signify sexual interest in someone.

To whistle in appreciation or sexual interest.

(sports) The blow of the whistle by the referee or other adjudicator signifying the end of the match.