* The train engineer blew his whistle as it approached the station. (This sentence uses "whistle" as a noun.)
* The little girl could whistle a perfect rendition of "Twinkle Twinkle Little Star." (This sentence uses "whistle" as a verb.)
* He was wearing a whistle around his neck, in case he needed to signal for help. (This sentence uses "whistle" as a noun referring to a specific object.)
* The wind whistled through the trees, making a mournful sound. (This sentence uses "whistle" as a verb, but in a figurative sense to describe the sound of the wind.)