<p><strong>Adjective</strong></p><ul><li>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 assistant.</li><li>Synonyms: effectual.</li><li>satisfactory and economical to use: Our new air conditioner is more efficient than our old one.</li><li>producing an effect, as a cause; causative.</li><li>utilizing a particular commodity or product with the least waste of resources or effort (usually used in combination): a fuel-efficient engine.</li></ul>