Efficacy

//ˈɛf.ɪ.kə.si// noun

noun ·Uncommon ·College level

Definitions

Noun
  1. 1
    The ability to produce a desired effect under ideal testing conditions. uncountable, usually

    "[…]and this hath even made me ſuſpect the efficacy of reliques, to examine the bones, queſtion the habits and appurtenances of Saints, and even of Chriſt himſelf."

  2. 2
    capacity or power to produce a desired effect wordnet
  3. 3
    A degree of ability to produce a desired effect; effectiveness. uncountable, usually

    "Toothbrush with improved efficacy"

Synonyms

All synonyms
effectivenessabilityavailabilitycalibercapabilitycapacity

Example

More examples

"Don't confuse "efficacy" with "efficiency"."

Etymology

From Old French efficace, from Late Latin efficācia (“efficacy”), from efficāx (“efficacious”); see efficacious.

Related phrases

self-efficacy

More for "efficacy"

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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.