Source : Webster's Revised Unabridged Dictionary (1913)

Whiffletree \Whif"fle*tree`\, n.
   Same as {Whippletree}.

Source : WordNet®

whiffletree
     n : a crossbar that is attached to the traces of a draft horse
         and to the vehicle or implement that the horse is pulling
         [syn: {whippletree}, {swingletree}]