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

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

Did you know?

Effective, effectual, and efficient are synonyms of efficacious, but each of these words has a slightly different connotation. Efficacious suggests possession of a special quality or virtue that makes it possible to achieve a result ("a detergent that is efficacious in removing grease"). Effective stresses the power to produce or the actual production of a particular effect ("an effective rebuttal"), while effectual suggests the accomplishment of a desired result, especially as viewed after the fact ("measures taken to reduce underage drinking have proved effectual"). The last synonym, efficient, implies an acting or potential for acting that avoids loss or waste of energy ("an efficient small car").

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 Over decades, UFAs have demonstrated their value by accelerating patients’ access to safe and efficacious medicines. Wayne Winegarden, Forbes, 15 June 2022 Seriously, who can say no to efficacious clean concealers and foundations? Kiana Murden, Vogue, 13 June 2022 Conversations on access and successfully treating psychiatric diagnoses often return to the question of efficacious medicines. Kathleen Frazier, Variety, 20 May 2022 Though the idea of the best clean concealers might conjure up depictions of serum-like dewy makeup formulas, Lawless’s concealer proves that even skin-friendly offerings can deliver an efficacious matte finish. Kiana Murden, Vogue, 18 May 2022 L'Occitane Known for botanical scents and pampering textures, L'Occitane's skincare and haircare products have also been multiple time GH Sustainability Award winners for their efficacious formulations and thoughtful, minimal waste packaging. April Franzino, Good Housekeeping, 28 Apr. 2022 The two-dose regimen didn’t prove as efficacious in protecting the youngest children from infection and disease, especially against the Omicron variant, as health officials had hoped. Alice Park, Time, 23 Mar. 2022 The cutting-edge Swiss skincare brand is famous for their impressively efficacious formulas and this assortment turns back the clock in style. Celia Shatzman, Forbes, 5 Nov. 2021 Because mRNA vaccines like Pfizer and Moderna need to be kept cold and their global supply is sparse, medical authorities instead used less efficacious but easier to transport vaccines like Sinovac, Johnson & Johnson and AstraZeneca. USA Today, 20 Mar. 2022 See More

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.

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

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

Dictionary Entries Near efficacious




See More Nearby Entries 

Statistics for efficacious

Last Updated

29 Jun 2022

Cite this Entry

“Efficacious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacious. Accessed 1 Jul. 2022.

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

More from Merriam-Webster on efficacious

Nglish: Translation of efficacious for Spanish Speakers


Test Your Vocabulary

Words Named After People

  • name tags
  • Namesake of the leotard, Jules Léotard had what profession?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

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