Efficacy
Synonyms: ability, adequacy, capableness, capacity, competence, effect, effectiveness, efficaciousness, efficiency, energy, force, influence, performance, potency, power, productiveness, strength, success, sufficiency, use, vigor, virtue, weight Notes: If something is efficacious, it is able to produce the desired result. Source: Roget's New Millennium Thesaurus Sign in to see full entry.