Source : Webster's Revised Unabridged Dictionary (1913)

Roundhouse \Round"house`\, n.
   1. A constable's prison; a lockup, watch-house, or station
      house. [Obs.]

   2. (Naut.)
      (a) A cabin or apartament on the after part of the
          quarter-deck, having the poop for its roof; --
          sometimes called the {coach}.
      (b) A privy near the bow of the vessel.

   3. A house for locomotive engines, built circularly around a
      turntable.

Source : WordNet®

roundhouse
     n 1: workplace consisting of a circular building for repairing
          locomotives
     2: a hook delivered with an exaggerated swing