Meaning of “whistle” - Learner’s Dictionary

whistle

verb uk us /ˈwɪsl/
MOUTH [ I, T ]

B2 to make a sound by breathing air out through a small hole made with your lips or through a whistle:

Someone whistled at her as she walked past.
WIND [ I ]

to produce a sound when air passes through a narrow space:

He could hear the wind whistling through the trees.

(Definition of “whistle verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)