Source : Webster's Revised Unabridged Dictionary (1913)

Bull-roarer \Bull"-roar`er\, n.
   A contrivance consisting of a slat of wood tied to the end of
   a thong or string, with which the slat is whirled so as to
   cause an intermittent roaring noise. It is used as a toy, and
   among some races in certain religious rites.