efficacy

noun

ef·​fi·​ca·​cy ˈe-fi-kə-sē How to pronounce efficacy (audio)
plural efficacies
: the power to produce an effect

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 on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Doctors also advise against this, noting episodic usage is not only dangerous but also will reduce the efficacy should the user need the drug in the future. Emily Burns, WWD, 7 Jan. 2025 However, critics question the efficacy of these measures. Kevin Lynn, Newsweek, 6 Jan. 2025 For example, the Digital Services Act in the European Union requires gaming companies who operate there to submit public-facing transparency reports about online harms within their spaces and the efficacy of their tools to combat them. Rachel Kowert, WIRED, 5 Jan. 2025 In addition to following Johnson’s medical treatment, Don’t Die compiles interviews with journalists, researchers, and doctors in the longevity field, all of whom have varying opinions about the efficacy of Johnson’s mission. Ct Jones, Rolling Stone, 3 Jan. 2025 See all Example Sentences for efficacy 

Word History

Etymology

borrowed from Latin efficācia, from efficāc-, efficāx "capable of fulfilling a function, efficacious" + -ia -y entry 2

First Known Use

1527, in the meaning defined above

Time Traveler
The first known use of efficacy was in 1527

Dictionary Entries Near efficacy

Cite this Entry

“Efficacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacy. Accessed 14 Jan. 2025.

Kids Definition

efficacy

noun
ef·​fi·​ca·​cy ˈef-i-kə-sē How to pronounce efficacy (audio)
plural efficacies
: the power to produce a desired result

More from Merriam-Webster on efficacy

Last Updated: - Updated example sentences
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