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[in-ef-i-key-shuh s]
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  1. not able to produce the desired effect; ineffective.
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Origin of inefficacious

First recorded in 1650–60; in-3 + efficacious
Related formsin·ef·fi·ca·cious·ly, adverbin·ef·fi·ca·cious·ness, in·ef·fi·cac·i·ty [in-ef-i-kas-i-tee] /ˌɪn ɛf ɪˈkæs ɪ ti/, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words


Examples from the Web for inefficacious

Historical Examples

  • Inefficacious they are not, unless they be too badly preached to obtain attention.

    Ralph the Heir

    Anthony Trollope

  • It was inefficacious, however, when one of these was involved in sin.

  • Is orthodoxy either so inefficacious or so moribund as you fancy?

  • But this plan of regulation was not only inefficacious, but unsafe.

  • And what do you think he's goin' to do with them inefficacious knick- knacks?

British Dictionary definitions for inefficacious


  1. failing to produce the desired effect
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Derived Formsinefficaciously, adverbinefficacy (ɪnˈɛfɪkəsɪ), inefficaciousness or inefficacity (ˌɪnɛfɪˈkæsɪtɪ), 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

Word Origin and History for inefficacious


1650s, from in- (1) "not, opposite of" + efficacious. Related: Inefficaciously; inefficaciousness (1640s).

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Online Etymology Dictionary, © 2010 Douglas Harper