Power to produce effects or intended results; effectiveness.
Power or capacity to produce a desired effect; effectiveness.
Efficacy is defined as the ability to do what is defined as desired or to be effective at producing a result.
An example of efficacy is when a crime bill is effective at stopping crime.
(uncountable) Ability to produce a desired amount of a desired effect.
Other Word Forms
Origin of efficacy
American Heritage Dictionary of the English Language, 5th Edition
From Old French efficace, from Late Latin efficacia (“efficacy”), from Latinefficax (“efficacious”); see efficacious.
Efficacy Sentence Examples
He was a firm believer in the efficacy of culture.
When its efficacy was not eternal, its effect was considered to endure for twenty years.
Thus he allowed the necessity of good works to salvation, but not in the old sense; proposed to allow the seven sacraments, but only as rites which had no inherent efficacy to salvation, and so on.
Just as the Mosaic dispensation came to an end with the appearance of Christ, so the sacraments of the new dispensation have lost their meaning and efficacy since the incarnation of God as Holy Spirit in the Amalricans.