Merriam-Webster's Collegiate® Dictionary, 11th Edition
WHISTLE
I. noun
Usage: often attributive
Etymology: Middle English, from Old English hwistle; akin to Old Norse hvīsla to whisper Date: before 12th century
1. a small wind instrument in which sound is produced by the forcible passage of breath through a slit in a short tube , a device through which air or steam is forced into a cavity or against a thin edge to produce a loud sound ,
2. a shrill clear sound produced by forcing breath out or air in through the puckered lips, the sound produced by a whistle, a signal given by or as if by whistling, a sound that resembles a whistle,
II. verb (whistled; whistling) Date: before 12th century intransitive verb
1. to utter a shrill clear sound by blowing or drawing air through the puckered lips, to utter a shrill note or call resembling a whistle, to make a shrill clear sound especially by rapid movement , to blow or sound a whistle,
2. to give a signal or issue an order or summons by or as if by whistling, to make a demand without result , transitive verb
1. to send, bring, signal, or call by or as if by whistling, to charge (as a basketball or hockey player) with an infraction, to produce, utter, or express by whistling , whistleable adjective