To make a shrill, high-pitched sound by forcing air through the mouth. To produce a whistling sound, restrictions to the flow of air are created using the teeth, tongue and lips.
Never whistle at a funeral.
To make a similar sound by forcing air through a musical instrument or a pipe etc.
The stream train whistled as it passed by.
To move in such a way as to create a whistling sound.
A bullet whistled past.
To send, signal, or call by a whistle.