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[trech-er-uh s] /ˈtrɛtʃ ər əs/
characterized by faithlessness or readiness to betray trust; traitorous.
deceptive, untrustworthy, or unreliable.
unstable or insecure, as footing.
dangerous; hazardous:
a treacherous climb.
Origin of treacherous
1300-50; Middle English trecherous < Anglo-French, equivalent to trecher deceiver (trech(ier) to deceive + -er -er2) + -ous -ous. Cf. French tricheur trickster
Related forms
treacherously, adverb
treacherousness, noun
untreacherous, adjective
untreacherously, adverb
untreacherousness, noun
1. unfaithful, faithless, treasonous. 2. deceitful.
1. loyal. 2. reliable. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for treacherous
Contemporary Examples
Historical Examples
  • This treacherous wind might continue for days and even weeks.

    A Woman who went to Alaska May Kellogg Sullivan
  • A man who was kind to a horse could not be treacherous to a man, Andrew decided.

    Way of the Lawless Max Brand
  • Your memory is treacherous, my dear monseigneur; look in another drawer.

    Louise de la Valliere Alexandre Dumas, Pere
  • It would be treacherous, now that he's helpless to forbid me.

    It Happened in Egypt C. N. Williamson
  • Of all human struggles there is none so treacherous and remorseless as the struggle between the artist man and the mother woman.

    Man And Superman George Bernard Shaw
British Dictionary definitions for treacherous


betraying or likely to betray faith or confidence
unstable, unreliable, or dangerous: treacherous weather, treacherous ground
Derived Forms
treacherously, adverb
treacherousness, 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
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Word Origin and History for treacherous

early 14c., from Old French trecheros (12c.), from trecheur, agent noun from trechier "to cheat, trick" (see trick). Figuratively, of things, from c.1600. Related: Treacherously; treacherousness.

Online Etymology Dictionary, © 2010 Douglas Harper
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