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 formstreach·er·ous·ly, adverbtreach·er·ous·ness, nounun·treach·er·ous, adjectiveun·treach·er·ous·ly, adverbun·treach·er·ous·ness, noun

Synonyms for treacherous

Antonyms for treacherous

1. loyal. 2. reliable. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for treacherous

Contemporary Examples of treacherous

Historical Examples of treacherous

  • Or he will be killed by falling stones or a treacherous blizzard.

    Ancient Man

    Hendrik Willem van Loon

  • A man who was kind to a horse could not be treacherous to a man, Andrew decided.

  • Mingwe was the name by which they were known to other tribes, and means "stealthy," "treacherous."

    The Trail Book

    Mary Austin

  • It would be treacherous, now that he's helpless to forbid me.

    It Happened in Egypt

    C. N. Williamson

  • The other gods knew that the treacherous Loki had done it, and did not blame Hodur.

    Classic Myths

    Mary Catherine Judd

British Dictionary definitions for treacherous



betraying or likely to betray faith or confidence
unstable, unreliable, or dangeroustreacherous weather; treacherous ground
Derived Formstreacherously, adverbtreacherousness, 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 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