The ratio of the output to the input of any system.

Roget 157: power; potency, potentiality; jiva^†; puissance, might, force, energy etc. 171; dint; right hand, right arm; ascendency^†, sway, control; prepotency, prepollence^†; almightiness, omnipotence; authority etc. 737; strength etc. 159.    ability; ableness etc. adj.^†; competency; efficacy; efficiency, productivity, expertise (skill) 698; validity, cogency; enablement^†; vantage ground; influence etc. 175.    pressure; conductivity; elasticity; gravity, electricity, magnetism, galvanism, voltaic electricity, voltaism, electromagnetism; atomic power, nuclear power, thermonuclear power; fuel cell; hydraulic power, water power, hydroelectric power; solar power, solar energy, solar panels; tidal power; wind power; attraction; vis inertiae [Lat.], vis mortua [Lat.], vis viva [Lat.]; potential energy, dynamic energy; dynamic friction, dynamic suction; live circuit, live rail, live wire.    capability, capacity; quid valeant humeri quid ferre recusent [Lat.]; faculty, quality, attribute, endowment, virtue, gift, property, qualification, susceptibility.    ... show more

Roget 644: utility; usefulness etc. adj.; efficacy, efficiency, adequacy; service, use, stead, avail; help etc. (aid) 707; applicability etc. adj.; subservience etc. (instrumentality) 631; function etc. (business) 625; value; worth etc. (goodness) 648; money's worth; productiveness etc. 168; cui bono [Lat.] etc. (intention) 620; utilization etc. (use) 677; step in the right direction.    common weal; commonwealth public good, public interest; utilitarianism etc. (philanthropy) 910.    ... show more

Skillfulness in avoiding wasted time and effort.

Dutch: rendement, doelmatigheid, efficiëntie