Pronunciation: (i-fish'unt),[key] —adj. 1. performing or functioning in the best possible manner with the least waste of time and effort; having and using requisite knowledge, skill, and industry; competent; capable: a reliable, efficient secretary. 2. satisfactory and economical to use: Our new air conditioner is more efficient than our old one. 3. producing an effect, as a cause; causative.
4. utilizing a particular commodity or product with maximum efficiency (usually used in combination): a fuel-efficient engine.