[ ef-i-kuh-see ]
/ ˈɛf ɪ kə si /
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noun, plural ef·fi·ca·cies.
capacity for producing a desired result or effect; effectiveness: a remedy of great efficacy.
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Test how much you really know about regular and irregular plural nouns with this quiz.
Question 1 of 9
Which of the following nouns has an irregular plural form?
Sometimes ef·fi·cac·i·ty [ef-i-kas-i-tee] /ˌɛf ɪˈkæs ɪ ti/ .
Origin of efficacy
OTHER WORDS FROM efficacynon·ef·fi·ca·cy, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022
How to use efficacy in a sentence
British Dictionary definitions for efficacy
/ (ˈɛfɪkəsɪ) /
the quality of being successful in producing an intended result; effectiveness
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012