n.
   - a clear, high-pitched sound made by forcing breath through a small hole between partly closed lips, or between one's teeth. ▸any similar sound. 
- an instrument used to produce such a sound, especially for giving a signal.
- Brit. informal a suit. 
[from rhyming sl. whistle and flute.]
v.
   - emit or produce a whistle. ▸produce (a tune) by whistling. ▸move rapidly through the air or a narrow opening with a whistling sound. 
- blow a whistle.
- 
(whistle for)
 wish for or expect (something) in vain.
Phrase
  
    - blow the whistle on
 informal bring (an illicit activity) to an end by informing on the person responsible.
- 
(as)
 clean as a whistle
 extremely clean or clear.
- whistle something down the wind
 - let go or abandon something.
- archaic turn a trained hawk loose by casting it off with the wind.
 
- whistle in the dark
 pretend to be unafraid.
 
  Derivative
  
  Etymology
  OE (h)wistlian (v.), (h)wistle (n.), of Gmc origin; imitative.