noun \ˈe-fi-kə-sē\

: the power to produce a desired result or effect

plural ef·fi·ca·cies

Full Definition of EFFICACY

:  the power to produce an effect

Examples of EFFICACY

  1. <questioned the efficacy of the alarms in actually preventing auto theft>
  2. 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

Origin of EFFICACY

(see efficacious)
First Known Use: 13th century


Next Word in the Dictionary: efficience
Previous Word in the Dictionary: efficacity
All Words Near: efficacy

Seen & Heard

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