What is Whistle?
Whistle is (noun) 1. a high sound made by blowing through your lips when they are almost closed She gave a whistle of surprise. We heard a whistle and saw a dog running across the field. 2. a simple instrument which makes a high sound, played by blowing He blew on his whistle to stop the match. (verb) 1. to blow through your lips to make a high sound They marched along, whistling an Irish song. The doorman whistled for a taxi. 2. to make a high sound using a small metal instrument The referee whistled to stop the match. 3. (of a bullet or the wind.) to make a loud high sound when moving fast
source: Easier English, Student Dictionary Upper Intermediate Level