1. Acting or producing effectively with a minimum of waste, expense, or unnecessary effort: an efficient builder; an efficient factory.
2. Acting directly to produce an effect: the efficient cause of the revolution.
3. Causing less waste or requiring less effort than comparable devices or methods. Used in combination: energy-efficient wind turbines; cost-efficient health care.
[Middle English, from Old French, from Latin efficiēns, efficient-, present participle of efficere, to effect; see EFFECT.]
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