whistlewhistlewhistles1noun1a small musical instrument that makes a long high sound when you blow it: The referee blew his whistle to end the match.2the long high sound that you make when you blow air out between your lips or when you blow a whistlewhistlewhistlewhistleswhistledwhistling2verb (whistles, whistling, whistled)to make a long high sound by blowing air out between your lips or through a whistle: He whistled a tune to himself.