efficacy

noun

ef·​fi·​ca·​cy ˈe-fi-kə-sē 

plural efficacies

: the power to produce an effect

Synonyms

• edge
• effectiveness
• effectualness
• efficaciousness
• efficacity
• efficiency
• productiveness

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

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

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

Kids Definition

efficacy

noun

ef·​fi·​ca·​cy ˈef-i-kə-sē 

plural efficacies

: the power to produce a desired result