Meaning of “whistle” - Learner’s Dictionary

whistle

noun [ C ] uk us /ˈwɪsl/
INSTRUMENT

B2 a small, simple instrument that makes a high sound when you blow through it:

The referee blew the whistle to end the game.
SOUND

the sound made by someone or something whistling

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