Source : Webster's Revised Unabridged Dictionary (1913)

Efficience \Ef*fi"cience\, Efficiency \Ef*fi"cien*cy\, n. [L.
   efficientia.]
   1. The quality of being efficient or producing an effect or
      effects; efficient power; effectual agency.

            The manner of this divine efficiency being far above
            us.                                   --Hooker.

   2. (Mech.) The ratio of useful work to energy expended.
      --Rankine.

   {Efficiency of a heat engine}, the ratio of the work done an
      engine, to the work due to the heat supplied to it.