[1] : WordNet (r) 2.0

whirr
     n : sound of something in rapid motion; "whir of a bird's
         wings"; "the whir of the propellers" syn: whir, whirring,
          birr
     v 1: make a soft swishing sound; "the motor whirred"; "the car
          engine purred" syn: whizz, whiz, whir, birr, purr
     2: make a vibrant sound, as of some birds syn: churr
see also:
whir whirring birr whizz whiz purr 
churr 

Whirr >> W Words
Whirr, definition of term: Whirr
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