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.
The American Dental Association says that 70 years of research backs up the safety and efficacy of adding fluoride to water, a process known as community water fluoridation. Jake Piazza, CNBC, 3 Nov. 2024 The longstanding goal of Drs. Walpole and Richardson was to take this groundbreaking compound and test its efficacy on the people who needed it most. Katie Hafner, Scientific American, 31 Oct. 2024 Future studies should take these into account to confirm vitamin K2's efficacy as a treatment for the condition. New Atlas, 30 Oct. 2024 The data showed good safety, tolerability and efficacy. Joshua P. Cohen, Forbes, 3 Nov. 2024 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 21 Nov. 2024.

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
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!