The Collaborative International Dictionary of English v.0.48:

Roundhouse \Round"house`\, n.
   1. A constable's prison; a lockup, watch-house, or station
      house. [Obs.]
      [1913 Webster]

   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.
          [1913 Webster]

   3. A house for locomotive engines, built circularly around a
      turntable.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "roundhouse":
   Long Melford, backhand, backhander, backstroke, boathouse,
   bolo punch, carbarn, carport, carriage house, fix-it shop, garage,
   hangar, haymaker, hook, one-two, repair shop, round-arm blow,
   short-arm blow, sidewinder, swing, uppercut