Source : Webster's Revised Unabridged Dictionary (1913)

Duple \Du"ple\, a. [L. duplus. See {Double}.]
   Double.

   {Duple ratio} (Math.), that in which the antecedent term is
      double the consequent, as of 2 to 1, 8 to 4, etc.

Source : WordNet®

duple
     adj : consisting of or involving two parts or components usually
           in pairs; "an egg with a double yolk"; "a double
           (binary) star"; "double doors"; "dual controls for
           pilot and copilot"; "duple (or double) time consists of
           two (or a multiple of two) beats to a measure" [syn: {double},
            {dual}]