efficacy
noun
ef·fi·ca·cy
ˈe-fi-kə-sē 
plural efficacies
: the power to produce a result or effect
increased teacher efficacy in classroom management
The efficacy of this treatment has not yet been proved.
In the upcoming … clinical trial, researchers will further investigate the efficacy and safety of the vaccine.—
Julia Landwehr
Julia LandwehrExamples 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
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 on the Web
Other technologies that could be phased out include waste heat recovery systems that pull heat from the car’s engine to the interior, solar reflective surface coating and high efficacy exterior lights.
—Julian Torres, CNN Money, 22 Feb. 2026
Blankfein’s vocal appreciation for the college experience comes at a time when some tech leaders are challenging the efficacy of higher ed.
—Emma Burleigh, Fortune, 20 Feb. 2026
So far, the data is limited on the efficacy of dry floating compared to wet floating.
—Shelby Hartman, Los Angeles Times, 18 Feb. 2026
Shaped by the contributions of nearly 70 volunteers, from civic leaders to Girl Scouts, her massive panels are a concrete reminder of the efficacy of our vote.
—Anya Sesay, jsonline.com, 16 Feb. 2026
See All Example Sentences for efficacy
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Julian Torres, CNN Money, 22 Feb. 2026
Blankfein’s vocal appreciation for the college experience comes at a time when some tech leaders are challenging the efficacy of higher ed.
—Emma Burleigh, Fortune, 20 Feb. 2026
So far, the data is limited on the efficacy of dry floating compared to wet floating.
—Shelby Hartman, Los Angeles Times, 18 Feb. 2026
Shaped by the contributions of nearly 70 volunteers, from civic leaders to Girl Scouts, her massive panels are a concrete reminder of the efficacy of our vote.
—Anya Sesay, jsonline.com, 16 Feb. 2026
See All Example Sentences for efficacy
Cite this Entry
“Efficacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacy. Accessed 24 Feb. 2026.
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