Flute
Whistle
noun
The kanji and the word are exactly the same. That means they share meanings as well.
Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word: Pretend you're trying to whistle, but you can't. All that comes out is air. You make a "Fuuuuuuueh" sound over and over, because you can't get the whole whistling thing down. Go ahead and pretend to do that (or do it for real).
そこで試合終了の笛が鳴ってしまった。
That's when the whistle blew to end the match.
公園を歩いていると、風とともに笛の音が聞こえてきました。
As I walked through the park, I heard the sound of a flute along with the wind.
あの男性は笛をピーピー鳴らしながらダンスをすることで有名です。
That man is famous for dancing while beeping his whistle.