[ ef-i-key-shuhs ]
See synonyms for: efficaciousefficaciouslyefficaciousness on Thesaurus.com

  1. capable of having the desired result or effect; effective as a means, measure, remedy, etc.: The medicine is efficacious in stopping a cough.

Origin of efficacious

First recorded in 1520–30; from Latin efficāci- (stem of efficax ) “effectual.” See efficient, -acious

Other words from efficacious

  • ef·fi·ca·cious·ly, adverb
  • ef·fi·ca·cious·ness, noun
  • non·ef·fi·ca·cious, adjective
  • non·ef·fi·ca·cious·ly, adverb
  • un·ef·fi·ca·cious, adjective
  • un·ef·fi·ca·cious·ly, adverb

Words Nearby efficacious

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use efficacious in a sentence

British Dictionary definitions for efficacious


/ (ˌɛfɪˈkeɪʃəs) /

  1. capable of or successful in producing an intended result; effective as a means, remedy, etc

Origin of efficacious

C16: from Latin efficāx powerful, efficient, from efficere to achieve; see effect

Derived forms of efficacious

  • efficaciously, adverb
  • efficaciousness, noun

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