whistle

noun

1. (countable, uncountable)A device designed to be placed in the mouth and blown, or driven by steam or some other mechanism, to make a whistling sound.

   “A lovely crisp exhaust: a feeling of almost unlimited power combined with complete freedom of running: and, to crown it all, a most melodious and wholly American chime whistle—these were my immediate impressions as we stormed rapidly out of Göttingen, intent on winning back some of the lost time.”

   “One thing I took great care to observe was obedience to the "whistle" boards which crop up with great frequency, for failure to sound the whistle, if observed by the gendarmerie, can bring about serious consequences.”

   “[...] and Temple station, which had to have a very modestly proportioned station building on the insistence of the Duke of Norfolk who owned the land on which it was built, and where the trains under the glass roof of the station were not allowed to blow their whistles, at the insistence of the barristers in the nearby Inns of Court.”

2. (countable, uncountable)An act of whistling.
3. (countable, uncountable)A shrill, high-pitched sound made by whistling.

   “We expressed our readiness, and in ten minutes were in the station wagon, rolling rapidly down the long drive, for it was then after nine.[…]As we reached the lodge we heard the whistle, and we backed up against one side of the platform as the train pulled up at the other.”

4. (countable, uncountable)Any high-pitched sound similar to the sound made by whistling.

   “the whistle of the wind in the trees”

5. (Cockney, countable, slang, uncountable)A suit (from whistle and flute).

   “We soldiers changed into our No.1 dress uniforms, Sid into his best whistle and we set off for the church.”

6. (colloquial, countable, uncountable)The mouth and throat; so called as being the organs of whistling.

   “Let's […] drink the other cup to wet our whistles.”

verb

1. (ambitransitive)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.

   “Never whistle at a funeral.”

   “He was whistling a happy tune.”

2. (ambitransitive)To make a similar sound by forcing air through a musical instrument or a pipe etc.

   “The steam train whistled as it passed by.”

   “It requires quite an orchestra to get a train to start; the guard blows his horn, the stationmaster rings a large bell, and the engine whistles.”

3. (intransitive)To move in such a way as to create a whistling sound.

   “A bullet whistled past.”

4. (transitive)To send, signal, or call by a whistle.
5. (intransitive, slang)To request admission to Opus Dei, a Roman Catholic organization.