any of various large hares of western North America, having very long hind legs and long ears.
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British Dictionary definitions for jack rabbit
any of various W North American hares, such as Lepus townsendi (white-tailed jack rabbit), having long hind legs and large ears
Word Origin for jack rabbit
C19: shortened from jackass-rabbit, referring to its long ears
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012