1. 
   boat whistle
   [n] - a whistle on a boat that is sounded as a warning
   Found op http://www.webdictionary.co.uk/definition.php?query=boat%20whistle
   
   
2. 
   boat whistle
   noun a whistle on a boat that is sounded as a warning
   Found op http://wordnetweb.princeton.edu/perl/webwn?s=boat%20whistle
   
   
3. 
   boatwhistle
   1) Harbor warning
   Found op http://www.mijnwoordenboek.nl/EN/crossword-dictionary/boatwhistle/1
   
   

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