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

Keep scrolling for more

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 This clean and efficacious serum from MARA absorb easily into skin, and feels like the fresh sea breeze after a thorough washing. Bianca Salonga, Forbes, "Skinmalism: Your Guide To The Biggest Beauty Trend For 2021," 19 Mar. 2021 Black women are at least two times as likely as white women to die during childbirth, and Black patients are consistently prescribed less efficacious drugs. Shenell Tolson, Quartz, "Why vaccination among Black Americans is so fraught," 12 Mar. 2021 No one was predicting vaccines that were highly efficacious by the end of the calendar year. USA Today, "Inside the night the NBA postponed their season," 11 Mar. 2021 Being able to bring a more deployable vaccine to a rural or poor community now would mean that more shots go into arms more quickly, compared to waiting to build infrastructure to protect the more fragile, more efficacious formulas. Maryn Mckenna, Wired, "The Pandemic Can’t End While Wealthy Nations Hoard Shots," 9 Mar. 2021 That’s because the vaccines aren’t 100% efficacious. Chris Smith, BGR, "CDC delays new coronavirus guidelines for vaccinated people," 6 Mar. 2021 The Johnson & Johnson vaccine is safe and highly efficacious, similar to the other COVID-19 vaccines that have already been authorized. Dr. Adjoa Smalls-mantey, ABC News, "Johnson & Johnson COVID-19 vaccine: Here's what to know," 28 Feb. 2021 The Food and Drug Administration reported Wednesday that Johnson & Johnson’s single-dose vaccine to protect against COVID-19 was safe and 72% efficacious in the United States, setting it up for a quick authorization process in the coming days. Cassidy Morrison, Washington Examiner, "FDA says Johnson & Johnson single-shot vaccine is safe and effective," 24 Feb. 2021 Those of you who have come to love the potent and efficacious lineup of products from Paula's Choice may be equally as enthused to know that shopping it just got a lot easier. Nykia Spradley, Allure, "Paula's Choice Skin Care Is Now Sold at Sephora," 25 Feb. 2021

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.

See More

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

Keep scrolling for more

Learn More about efficacious

Time Traveler for efficacious

Time Traveler

The first known use of efficacious was in 1528

See more words from the same year

Listen to Our Podcast about efficacious

Statistics for efficacious

Last Updated

25 Mar 2021

Cite this Entry

“Efficacious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacious. Accessed 14 Apr. 2021.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

Keep scrolling for more

More Definitions for efficacious



English Language Learners Definition of efficacious

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

More from Merriam-Webster on efficacious

Thesaurus: All synonyms and antonyms for efficacious

Nglish: Translation of efficacious for Spanish Speakers

Comments on efficacious

What made you want to look up efficacious? Please tell us where you read or heard it (including the quote, if possible).


Test Your Vocabulary

The Exceptions Quiz III

  • one green toy robot amidst many red toy robots
  • Which of these words does not mean "nonsense"?
Spell It

Can you spell these 10 commonly misspelled words?

 AlphaBear 2

Spell words. Make bears.

Love words? Need even more definitions?

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