efficacy

C2+ Topic:Cause, Change & Process

US /ˈɛfɪkəsi/ UK /ˈɛfɪkəsi/ See IPA manual

noun

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... effectiveness potencyefficaciousnessefficacity power success

Opposites

inefficacyineffectivenessimpotence

Word family

Related forms efficacious efficacity effect

Etymology

From Latin efficācia ('efficacy, power'), from efficāx ('effective'), from efficere ('to accomplish'), from ex- ('out') + facere ('to make').

efficācia Latin efficāx Latin facere Latin

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Topics

Cause, Change & Process Word Formation & Derivatives

# 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

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