[ ef-i-kuh-see ]
/ ˈɛf ɪ kə si /

noun, plural ef·fi·ca·cies.

capacity for producing a desired result or effect; effectiveness: a remedy of great efficacy.

Origin of efficacy

1520–30; < Latin efficācia, equivalent to efficāc- (see efficacious) + -ia -y3
Related formsnon·ef·fi·ca·cy, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for efficacies


/ (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

Word Origin and History for efficacies



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.

Online Etymology Dictionary, © 2010 Douglas Harper