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1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   Quadruplex \Quad"ru*plex\, a. [L., from quattuor four + plicare
      to fold.]
      Fourfold; folded or doubled twice.
      [1913 Webster]
      Quadruplex system (Electric Telegraph), a system by which
         four messages, two in each direction, may be sent
         simultaneously over the wire.
         [1913 Webster]