Source : Webster's Revised Unabridged Dictionary (1913)

Whippletree \Whip"ple*tree`\, n. [See {Whip}, and cf.
   {Whiffletree}.]
   1. The pivoted or swinging bar to which the traces, or tugs,
      of a harness are fastened, and by which a carriage, a
      plow, or other implement or vehicle, is drawn; a
      whiffletree; a swingletree; a singletree. See
      {Singletree}.

            [People] cut their own whippletree in the woodlot.
                                                  --Emerson.

   2. (Bot.) The cornel tree. --Chaucer.

Source : WordNet®

whippletree
     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: {whiffletree}, {swingletree}]