1.verbTo 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."
2.verbTo make a similar sound by forcing air through a musical instrument or a pipe etc.
"The stream train whistled as it passed by."
3.verbTo move in such a way as to create a whistling sound.