Index of English words, starting with "ef"

(1) - Efficacious (n.) Possessing the quality of being effective; productive of, or powerful to produce, the effect intended; as, an efficacious law.

(1) - Efficacy (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.

(1) - Efficiency (n.) The ratio of useful work to energy expended.
(2) - Efficiency (n.) The quality of being efficient or producing an effect or effects; efficient power; effectual agency.