Source : Webster's Revised Unabridged Dictionary (1913)

Duplex \Du"plex\, a. [L., fr. duo two + plicare to fold. See
   {Two}, and {Complex}.]
   Double; twofold.

   {Duplex escapement}, a peculiar kind of watch escapement, in
      which the scape-wheel has two sets of teeth. See
      {Escapement}.

   {Duplex lathe}, one for turning off, screwing, and surfacing,
      by means of two cutting tools, on opposite sides of the
      piece operated upon.

   {Duplex pumping engine}, a steam pump in which two steam
      cylinders are placed side by side, one operating the
      valves of the other.

   {Duplex querela} [L., double complaint] (Eccl. Law), a
      complaint in the nature of an appeal from the ordinary to
      his immediate superior, as from a bishop to an archbishop.
      --Mozley & W.

   {Duplex telegraphy}, a system of telegraphy for sending two
      messages over the same wire simultaneously.

   {Duplex watch}, one with a duplex escapement.