efficience

ef`fi´cience

(ĕf`fĭsh´ens)
n.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.
efficiency of a heat engine
the ratio of the work done by an engine, to the work due to the heat supplied to it.