\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.