noun, plural ef·fi·ca·cies.
Examples from the Web for efficacy
On average, the vaccine has an efficacy of about 60 percent.When You Get the Flu This Winter, You Can Blame Anti-Vaxxers|Kent Sepkowitz|January 1, 2015|DAILY BEAST
The efficacy of bandying threats of going to hell met its match in the Civil War.
Most Pennsylvanians now support a moratorium on capital punishment until its efficacy can be determined.
But the conditions on the ground in Syria are not the same, and cast great doubt on the efficacy of airstrikes.
Over the next few years, local governments will make decisions that will determine their long-term solvency and efficacy.Why Progressives Shouldn’t Support Public Workers Unions|Dmitri Mehlhorn|July 11, 2014|DAILY BEAST
They estimate the efficacy of prayer by its quantity and not by its quality.Wit and Humor of the Bible|Marion D. Shutter
Of course there are some reservations to be made in the details of this way of explaining the efficacy of sacrificial banquets.The Elementary Forms of the Religious Life|Emile Durkheim
It must therefore be taken as a tax paid for the efficacy supposed to be communicated to the other branch—the 'duty to man.'The English Utilitarians, Volume II (of 3)|Leslie Stephen
"We, out here, don't believe much in the efficacy of blue blood," he said contemptuously.Wolf Breed|Jackson Gregory
We hope we have now heard enough about the efficacy of wealth for poetry, and to make poets happy.Life of Robert Burns|Thomas Carlyle
British Dictionary definitions for efficacy
Word Origin and History for efficacy
1520s, from Latin efficacia "efficacy, efficiency," from efficax (genitive efficacis) "powerful, effective," from stem of efficere "work out, accomplish" (see effect). Earlier in same sense was efficace (c.1200), from Old French eficace (14c.), from Latin efficacia; also efficacite (early 15c.), from Latin efficacitatem.