efficacy C2+ Topic:Cause, Change & Process US /ˈɛfɪkəsi/ UK /ˈɛfɪkəsi/ See IPA manual Meanings 1 noun the ability to produce a desired or intended result Clinical trials confirmed the vaccine's efficacy against the virus. Thesaurus Synonyms 1 noun · the ability to produce a... effectivenesspotencyefficaciousnessefficacitypowersuccess ↔ Opposites inefficacyineffectivenessimpotence Word family Related forms efficaciousefficacityeffect Etymology AI details From Latin efficācia ('efficacy, power'), from efficāx ('effective'), from efficere ('to accomplish'), from ex- ('out') + facere ('to make'). efficācia Latin efficāx Latin facere Latin View etymology graph -> Topics Cause, Change & Process Word Formation & Derivatives External links Cambridge Dictionary Wiktionary Google Images # efficacy **Type:** Word **Level:** C2+ **Part of speech:** noun **IPA (US):** /ˈɛfɪkəsi/ **IPA (UK):** /ˈɛfɪkəsi/ ## Meanings 1. the ability to produce a desired or intended result ## Examples - Clinical trials confirmed the vaccine's efficacy against the virus. ## Synonyms - effectiveness - potency - efficaciousness - efficacity - power - success ## Antonyms - inefficacy - ineffectiveness - impotence ## Related Forms - efficacious - efficacity - effect ## Roots and Affixes - Root: efficācia - Root: efficāx - Root: facere ## Etymology From Latin efficācia ('efficacy, power'), from efficāx ('effective'), from efficere ('to accomplish'), from ex- ('out') + facere ('to make'). ## AI Etymology Efficacy is from Latin efficācia ('efficacy, power'), from efficāx ('effective'), from efficere ('to accomplish'), from ex- ('out') + facere ('to make'). Important recorded forms include efficācia (Latin), efficāx (Latin), and facere (Latin). Morphologically, the word is a built form whose named elements carry part of the historical sense. The current sense covers the ability to produce a desired or intended result. The wider family includes related words such as efficacious, efficacity, and effect. ## Topics - Cause, Change & Process - Word Formation & Derivatives markdown