[fuh-ley-shuh s]


containing a fallacy; logically unsound: fallacious arguments.
deceptive; misleading: fallacious testimony.
disappointing; delusive: a fallacious peace.

Origin of fallacious

First recorded in 1500–10, fallacious is from the Latin word fallāciōsus deceitful, deceptive. See fallacy, -ous
Related formsfal·la·cious·ly, adverbfal·la·cious·ness, nounnon·fal·la·cious, adjectivenon·fal·la·cious·ly, adverbnon·fal·la·cious·ness, nounun·fal·la·cious, adjectiveun·fal·la·cious·ly, adverb
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for fallacious

Contemporary Examples of fallacious

  • But such disparagement was itself a kneejerk reaction, and it was fallacious.

    The Daily Beast logo
    The Cult of Royal Porn

    Tim Teeman

    April 26, 2014

Historical Examples of fallacious

  • Still, through this fallacious medium, a real enlargement of ideas is attained.

  • Only what must be avoided are fallacious inferences, my dear Lena—especially at this hour.


    Joseph Conrad

  • Political reconciliations are but outward and hollow, and fallacious.

    Apologia Pro Vita Sua

    John Henry Cardinal Newman

  • There has never been a religion too gross, too fallacious, to fail of followers.

  • No compromise for him, no evasions, no fallacious, unsecured promises to pay.

    Dream Days

    Kenneth Grahame

British Dictionary definitions for fallacious



containing or involving a fallacy; illogical; erroneous
tending to mislead
delusive or disappointinga fallacious hope
Derived Formsfallaciously, adverbfallaciousness, 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 fallacious

c.1500, from fallacy (Latin fallacia) + -ous. Related: Fallaciously; fallaciousness.

Online Etymology Dictionary, © 2010 Douglas Harper