To whistle means to make a high, musical sound by forcing air through your lips when they're shaped in a small, tight circle. You might whistle a cheerful tune while walking to school, or whistle to get someone's attention across a playground. Some people can whistle incredibly loudly by putting their fingers in their mouth, though this takes practice to master.

A whistle is also a small device that makes a sharp, piercing sound when you blow air through it. Referees use whistles to stop play during soccer or basketball games. Train conductors once used whistles to signal departure. A tea kettle whistles when the water inside boils, and a factory whistle might announce the end of a work shift.

The word can describe any high, airy sound: wind whistles through cracks in a window, and an arrow whistles through the air.

When someone whistles past something, they're moving by it quickly, like when a bicyclist whistles past you on the sidewalk. And if you achieve something impressive with little effort, you might say you did it whistling, meaning it felt easy and enjoyable.