Source : Webster's Revised Unabridged Dictionary (1913)

Axletree \Ax"le*tree`\, n. [Cf. Icel. ["o]xultr?.]
   1. A bar or beam of wood or iron, connecting the opposite
      wheels of a carriage, on the ends of which the wheels
      revolve.

   2. A spindle or axle of a wheel. [Obs.]

Source : WordNet®

axletree
     n : a dead axle on a carriage or wagon that has terminal
         spindles on which the wheel revolve