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. <mechanics> The ratio of useful work to energy expended. Efficiency of a heat engine, the ratio of the work done an engine, to the work due to the heat supplied to it.

Origin: L. Efficientia.

(01 Mar 1998)