ef·​fi·​ca·​cious | \ ˌe-fə-ˈkā-shəs How to pronounce efficacious (audio) \

Definition of efficacious

: having the power to produce a desired effect an efficacious remedy

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Other Words from efficacious

efficaciously adverb
efficaciousness noun

Choose the Right Synonym for efficacious

effective, effectual, efficient, efficacious mean producing or capable of producing a result. effective stresses the actual production of or the power to produce an effect. an effective rebuttal effectual suggests the accomplishment of a desired result especially as viewed after the fact. the measures to stop the pilfering proved effectual efficient suggests an acting or a potential for action or use in such a way as to avoid loss or waste of energy in effecting, producing, or functioning. an efficient small car efficacious suggests possession of a special quality or virtue that gives effective power. a detergent that is efficacious in removing grease

Examples of efficacious in a Sentence

taking a cookie break while studying is one of the most efficacious ways of rejuvenating the mind that I have ever discovered
Recent Examples on the Web Yet many institutions continue pouring millions of dollars into a bloated and largely futile diversity apparatus, while bypassing far more efficient and efficacious models. Pamela Newkirk, WSJ, "After 2020, How Do We Move Forward on Race?," 14 Dec. 2020 So far, the results—which were published in The New England Journal of Medicine today—have shown that the vaccine is 95 percent efficacious at protecting adults. James Hamblin, The Atlantic, "America's First COVID-19 Vaccine Is Here," 10 Dec. 2020 The vaccine won’t be efficacious until the second dose is administered, Welsh officials emphasized Friday when alerting citizens that the first shots will be given on Tuesday. Joel Gehrke, Washington Examiner, "World Health Organization officials intrigued by 'e-vaccination certificate'," 4 Dec. 2020 US Food and Drug Administration officials have promised not to grant emergency use authorization to any vaccine that has not been proven both safe and efficacious. David Williams, CNN, "'Black Panther' star Letitia Wright faces backlash for posting video criticizing coronavirus vaccines," 4 Dec. 2020 There have been hardly any vaccine studies, for instance, which raises another question: How will African countries deal with vaccines that have been shown to be efficacious on other continents? Kai Kupferschmidt, Science | AAAS, "First-of-its-kind African trial tests common drugs to prevent severe COVID-19," 3 Dec. 2020 The efficacious mouthwashes — which included Listerine Antiseptic, Orajel Antiseptic Rinse, and Crest Pro‐Health — appeared to kill more than 99.9% of the virus after 30 seconds or more of gargling and swishing. Molly Longman, refinery29.com, "What You Really Need To Know About COVID-19 & Mouthwash," 5 Nov. 2020 Although the vaccine appeared less efficacious than candidates being developed by Moderna and jointly by Pfizer and BioNTech, the news was welcomed by physicians and scientists. Washington Post, "A Thanksgiving marked by surging covid-19 cases and questions about a leading vaccine candidate," 27 Nov. 2020 Pfizer and BioNTech said further data showed that their vaccine for covid-19 was 95% effective, and similarly efficacious in people over 65. The Economist, "Business this week," 21 Nov. 2020

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

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First Known Use of efficacious

1528, in the meaning defined above

History and Etymology for efficacious

borrowed from Middle French efficace "effective" or its source Latin efficāc-, efficāx "capable of fulfilling a function, effective" (from efficere "to make, bring about, produce, carry out" + -āc-, -āx, deverbal suffix denoting habitual or successful performance) + -ious — more at effect entry 1, audacious

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The first known use of efficacious was in 1528

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Last Updated

25 Dec 2020

Cite this Entry

“Efficacious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacious. Accessed 24 Jan. 2021.

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How to pronounce efficacious (audio)

English Language Learners Definition of efficacious

formal : having the power to produce a desired result or effect

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