What is whistle? What is whistle? To produce a clear musical sound by forcing air through the teeth or through an aperture formed by pursing the lips.To produce a clear, shrill, sharp musical sound by blowing on or through a device.To produce a high-pitched sound when moving swiftly through the air: The stone whistled past my head. To produce a high-pitched sound by the rapid movement of air through an opening or past an obstruction: Wind whistled through the cracks in the windows. To emit a shrill, sharp, high-pitched cry, as some birds and other animals.To produce by whistling: whistle a tune. To summon, signal, or direct by whistling.To cause to move with a whistling noise.A small wind instrument for making whistling sounds by means of the breath.A device for making whistling sounds by means of forced air or steam: a factory whistle. A sound produced by a whistling device or by whistling through the lips.A whistling sound, as of an animal or a projectile.The act of whistling.A whistling sound used to summon or command.blow the whistle Slang To expose a wrongdoing in the hope of bringing it to a halt: an attorney who blew the whistle on governmental corruption. whistle in the dark To attempt to keep one's courage up.