(n.) Power to produce effects; operation or energy of an agent or force; production of the effect intended; as, the efficacy of medicine in counteracting disease; the efficacy of prayer.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). efficacy. Retrieved September 20, 2026, from http://smartdefine.org/efficacy/definitions/2001756 |
| Chicago | Webster's. 2011. "efficacy" http://smartdefine.org/efficacy/definitions/2001756 (accessed September 20, 2026). |
| Harvard | Webster's 2011, efficacy, Smart Define, viewed 20 September, 2026, <http://smartdefine.org/efficacy/definitions/2001756>. |
| MLA | Webster's. "efficacy" 27 May 2011. Web. 20 September 2026. <http://smartdefine.org/efficacy/definitions/2001756> |