1. (n.) Producing an effect with minimum expense of time, effort, or skill\; efficient power; effectual agency.

2. (n.) The ratio of useful work to energy expended.

ability able ableness address adept adeptness adequacy adroitness airmanship applicability artfulness artisanship artistry availability bravura brilliance caliber capability capable capableness capacity cleverness command competence competent control coordination craft craftsmanship cunning deftness dexterity dexterousness dextrousness diplomacy effectiveness effectual efficacious efficaciousness efficacy efficient experience expert expertise expertness facility faculty finesse fitness fitted flair functionality genius grace grip handiness helpfulness horsemanship ingeniousness ingenuity know-how marksmanship masterly mastership mastery operability performance potency practicability practical ability practical utility practicality productivity proficiency proficient profitability prowess qualification qualified quickness readiness resource resourcefulness savoir-faire savvy seamanship serviceability skill skilled skillful skillfulness style sufficiency susceptibility tact tactfulness talent technical brilliance technical mastery technical skill technique the goods the stuff timing usability use usefulness utility utilizability virtuosity virtuous what it takes wit wizardry workmanship