efficacy

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noun ef·fi·ca·cy \ ˈe-fi-kə-sē \

Definition of efficacy

plural efficacies

:the power to produce an effect

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Examples of efficacy in a Sentence

In the planner's view, Rumsfeld had two goals: to demonstrate the efficacy of precision bombing and to "do the war on the cheap." —Seymour M. Hersh, New Yorker, 7 Apr. 2003
Vaccines exist, but their efficacy against aerosolized plague is unknown. —Sharon Begley et al., Newsweek, 8 Oct. 2001
… efficacy does not have to be demonstrated before homeopathic products are marketed. —Alison Abbott et al., Nature, 26 Sept. 1996
questioned the efficacy of the alarms in actually preventing auto theft

Recent Examples of efficacy from the Web

A review of meetings' records shows the group itself occasionally wrestled with its identity – and efficacy – and took up reform ideas that ultimately went nowhere.

— matthew glowicki, The Courier-Journal, "If Louisville's police watchdog group is a bulldog that 'cannot bite,' is it relevant?," 28 Aug. 2017
How did a man who understood better than most the relative safety and efficacy of inoculation choose wrong?

— stephen coss, Smithsonian, "What Led Benjamin Franklin to Live Estranged From His Wife for Nearly Two Decades?," 24 Aug. 2017
The Food and Drug Administration (FDA) has done a bit of a U-turn on Pfizer's Mylotarg, an acute myeloid leukemia (AML) treatment that the company voluntarily withdrew from the market after follow-up research failed to prove its safety and efficacy.

— Fortune, "Brainstorm Health Daily: July 12, 2017," 12 July 2017
These are closely related viruses and the existing vaccine should have efficacy against Powassan.

— durland fish, Fortune, "This Tick-Borne Virus Could Be Worse Than Lyme Disease," 3 July 2017
Though the survey, involving 2,897 medical cannabis patients, didn’t track actual drug use or efficacy, the findings fits with previous data.

— beth mole, Ars Technica, "Survey: Pain patients overwhelmingly prefer medical marijuana over opioids," 29 June 2017
In a study conducted in Sudan in 2015, a single dose offered 80% protection during the first 2 months—although some participants may have been exposed to cholera the year before, essentially making the vaccine a booster and increasing its efficacy.

— kai kupferschmidt, Science | AAAS, "Cholera vaccine faces major test in war-torn Yemen," 28 June 2017
The trio of shootings this week, however, served as a newsflash that there was still work to be done, raising questions about the efficacy of security efforts downtown.

— allie gross, Detroit Free Press, "Detroit Police Chief James Craig: Fireworks a success, despite separate shootings," 27 June 2017
The curriculum is specifically designed toward fostering character development and responsibility geared to elevating individual empowerment, efficacy and self-esteem.

— miamiherald, "Carlson Gracie Jiu-Jitsu medals at Miami Spring International," 25 June 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'efficacy.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Origin and Etymology of efficacy

see efficacious

NEW! Time Traveler

First Known Use: 13th century

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efficacy Synonyms

Synonyms

edge, effectiveness, effectualness, efficaciousness, efficacity, efficiency, productiveness

Antonyms

ineffectiveness, ineffectuality, ineffectualness, inefficiency

Related Words

ability, capability, capacity; potency, puissance, strength

Near Antonyms

inability, inadequacy, inadequateness, incompetence, incompetency

EFFICACY Defined for English Language Learners

efficacy

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noun

Definition of efficacy for English Language Learners

: the power to produce a desired result or effect

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Thesaurus: All synonyms and antonyms for efficacy Spanish Central: Translation of efficacy Nglish: Translation of efficacy for Spanish speakers Britannica English: Translation of efficacy for Arabic speakers Britannica.com: Encyclopedia article about efficacy

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efficacy

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efficacy

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