The Collaborative International Dictionary of English v.0.48:

Reducing \Re*du"cing\ (r?*d?"s?ng),
   a & n. from Reduce.
   [1913 Webster]

   Reducing furnace (Metal.), a furnace for reducing ores.

   Reducing pipe fitting, a pipe fitting, as a coupling, an
      elbow, a tee, etc., for connecting a large pipe with a
      smaller one.

   Reducing valve, a device for automatically maintaining a
      diminished pressure of steam, air, gas, etc., in a pipe,
      or other receiver, which is fed from a boiler or pipe in
      which the pressure is higher than is desired in the
      receiver.
      [1913 Webster]