whistle

Etymology 1

From Middle English whistel, whistil, whistle, from Old English hwistle, from the verb (see below).

noun

1. 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. 1960 October, P. Ransome-Wallis, “Modern motive power of the German Federal Railway: Part Two”, in Trains Illustrated, page 611
   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. 1961 March, ""Balmore"", “Driving and firing modern French steam locomotives”, in Trains Illustrated, page 151
   … 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. 2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, pages 61–62
2. An act of whistling.
3. A shrill, high-pitched sound made by whistling.
4. Any high-pitched sound similar to the sound made by whistling.
   the whistle of the wind in the trees
5. (Cockney rhyming slang) 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. 2005, Wally Payne, A Minority of One: A Monkey's Tale Continued
6. (colloquial) The mouth and throat; so called as being the organs of whistling.

Etymology 2

From Middle English whistlen, from Old English hwistlan, hwistlian (“to whistle”), from Proto-West Germanic *hwistlōn, from Proto-Germanic *hwistlōną (“to make a hissing sound”). Cognate with Icelandic hvísla (“to whisper”), Russian свистеть (svistetʹ, “to whistle”).

verb

1. (transitive, intransitive) 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.
   She was whistling a happy tune.
2. (transitive, intransitive) 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. 1941 February, Voyageur, “The Railways of Greece”, in Railway Magazine, page 67
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.