from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. Power or capacity to produce a desired effect; effectiveness.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. Ability to produce a desired amount of a desired effect.

from the GNU version of the Collaborative International Dictionary of English

  • n. Power to produce effects; operation or energy of an agent or force; production of the effect intended

from The Century Dictionary and Cyclopedia

  • n. The quality of being efficacious or effectual; production of, or the capacity of producing, the effect intended or desired; effectiveness.
  • n. Synonyms Efficiency, etc. (see effectiveness); virtue, force, energy.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. capacity or power to produce a desired effect


Latin efficācia, from efficāx, efficāc-, efficacious; see efficacious.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Latin efficacia ("efficacy"), from efficax ("efficacious"); see efficacious. (Wiktionary)



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  • Don't confuse with effective. They will know that you are impersonating a serious grad student.

    June 28, 2008