noun
Uncommon
efficacy
EHF-ih-kuh-see
Efficacy (noun) means the power to produce a desired result, especially under controlled or ideal conditions. Example: “Clinical trials confirmed the drug's efficacy against the virus.”
noun
1
The power to produce a desired result, especially under controlled or ideal conditions.
"Clinical trials confirmed the drug's efficacy against the virus."
"The report questioned the efficacy of the new training program."
"Scientists tested the efficacy of the new cleaning spray in the laboratory."
How to use efficacy
Learner’s notesIn plain EnglishHow well something works in practice, especially when tested scientifically or formally.
When to use it
A more formal, technical word than "effectiveness" — common in medical and scientific writing.
Easily confused with
Common pairings
clinical efficacy
proven efficacy
vaccine efficacy
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Word forms
- Plural
- efficacies
Fill the gap
Can you complete this real example?
Clinical trials confirmed the drug's _____ against the virus.
Etymology
From Late Latin efficacia, related to efficax, "capable of producing an effect."
Synonyms
View more →Antonyms
inefficacy
Related words
Rhymes for efficacy
See all rhymes for efficacy →Frequently asked questions
What does “efficacy” mean?
The word “efficacy” means the power to produce a desired result, especially under controlled or ideal conditions. In plain terms, how well something works in practice, especially when tested scientifically or formally.
How do you pronounce “efficacy”?
“Efficacy” is pronounced EHF-ih-kuh-see (/ˈɛf.ɪ.kə.si/ in IPA).
How do you use “efficacy” in a sentence?
Here is “efficacy” used in a sentence: “Clinical trials confirmed the drug's efficacy against the virus.”
What is another word for “efficacy”?
Words with a similar meaning to “efficacy” include efficacity.
What part of speech is “efficacy”?
“Efficacy” is a noun.
Where does the word “efficacy” come from?
The word “efficacy” comes from Late Latin. From Late Latin efficacia, related to efficax, "capable of producing an effect.".
Is “efficacy” a common word?
“Efficacy” is an uncommon word in modern English.
What is the difference between efficacy and effectiveness?
Efficacy refers to the power of something to produce a desired result under controlled or ideal conditions, such as in a clinical trial. Effectiveness describes how well something works in real-world, everyday conditions, which can differ from its performance under ideal test conditions.
What is the difference between efficacy and efficiency?
Efficacy is about whether something achieves the desired result at all, while efficiency is about how economically it does so, in terms of time, effort, or resources. A treatment can have high efficacy but low efficiency if it works well but requires excessive resources.
Is efficacy used mainly in formal or technical contexts?
Efficacy is generally used in formal, scientific, or medical contexts rather than casual conversation. It commonly appears in phrases like "clinical efficacy" or "vaccine efficacy."
