Merriam-Webster Logo
SINCE 1828
Menu
dictionary thesaurus

Thesaurus

efficacy

noun

Synonyms and Antonyms of efficacy

the power to produce a desired result

  • questioned the efficacy of the alarms in actually preventing auto theft
Synonyms of efficacy

edge, effectiveness, effectualness, efficaciousness, efficacity, efficiency, productiveness
Words Related to efficacy

ability, capability, capacity

potency, puissance, strength
Near Antonyms of efficacy

inability, inadequacy, inadequateness, incompetence, incompetency
Antonyms of efficacy

ineffectiveness, ineffectuality, ineffectualness, inefficiency

Learn More about efficacy

  1. Dictionary: Definition of efficacy Spanish Central: Translation of efficacy Nglish: Translation of efficacy for Spanish speakers Britannica English: Translation of efficacy for Arabic speakers Britannica.com: Encyclopedia article about efficacy

Seen and Heard

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

show comments hide comments

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

WORD OF THE DAY

perforce

by force of circumstances

Get Word of the Day daily email!

TRENDING NOW

  1. gaslight It is a word, though.

  2. invasion CNN reporter questions President.

  3. relevancy Ariana Grande slams ex-fiancé.

SEE ALL

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Words at Play

Ask the Editors

Word Games