Word
efficacy
Phoneticsef·fi·ca·cy, stress on the first syllable
US/ˈɛfɪˌkæsi/
UK/ˈɛfɪkəsi/
Definitions
01general effectiveness
C1 · Advanced Uncountable noun Formal
n. the ability of something to produce the result that was intended.
n. the capacity for producing a desired result or effect. Often used in formal contexts to discuss the success of policies, treatments, or methods.
“The committee questioned the efficacy of the new rules in reducing office waste.”
“Public health officials debated the efficacy of the proposed intervention, citing a lack of longitudinal data to support such a drastic change in policy.”
Pitfall
The efficacy for the new law was high.
The efficacy of the new law was high.
Use the preposition 'of' to connect efficacy to the thing being measured.
Synonyms
Antonyms
02medical/scientific testing
C1 · Advanced Uncountable noun Medicine Technical
n. how well a drug or treatment works in a controlled scientific test.
n. the performance of an intervention under ideal and controlled circumstances, such as a clinical trial. It is distinct from 'effectiveness', which refers to performance in real-world settings.
“The new vaccine showed high efficacy in the first stage of clinical trials.”
“While the drug demonstrated significant efficacy in laboratory settings, its real-world effectiveness was hampered by poor patient compliance and storage requirements.”
Real-World Examples
“Within the current work, the research team closely investigated eugenol, clove oil's dominant bioactive component, to understand its action and further assess its safety and efficacy.” “This provides information about efficacy and can reveal patterns, such as when symptoms are most severe and if they change month to month.” Etymology
From Old French efficace, from Late Latin efficācia (“efficacy”), from efficāx (“efficacious”); see efficacious.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
Related words
- Exam level
- CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.C1 AdvancedIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.7.0–8.0TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 5.0–5.595–113TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.945–990
- Frequency
- Frequent
- Level
- C1 · Advanced
- Updated
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