[in-ef-i-key-shuh s]


not able to produce the desired effect; ineffective.

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 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for inefficacious

Historical Examples of inefficacious

British Dictionary definitions for inefficacious



failing to produce the desired effect
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).

Online Etymology Dictionary, © 2010 Douglas Harper