1. noun /wɪsl̩/
a) A device designed to be placed in the mouth in order to make a whistling sound.
We soldiers changed into our No.1 dress uniforms, Sid into his best whistle and we set off for the church.
b) An act of whistling.
2. verb /wɪsl̩/
a) 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.
A bullet whistled past.
b) To move in such a way as to create a whistling sound.
Wikipedia foundation.