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Synonyms

treacherous

American  
[trech-er-uhs] / ˈtrɛtʃ ər əs /

adjective

  1. characterized by faithlessness or readiness to betray trust; traitorous.

    Synonyms:
    treasonous, faithless, unfaithful
    Antonyms:
    loyal

  2. deceptive, untrustworthy, or unreliable.

    Synonyms:
    deceitful
    Antonyms:
    reliable

  3. unstable or insecure, as footing.

  4. dangerous; hazardous.

    a treacherous climb.
treacherous British  
/ ˈtrɛtʃərəs /

adjective

  1. betraying or likely to betray faith or confidence

  2. unstable, unreliable, or dangerous

    treacherous weather

    treacherous ground
"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

Other Word Forms

  • treacherously adverb
  • treacherousness noun
  • untreacherous adjective
  • untreacherousness noun

Etymology

Origin of treacherous

First recorded in 1300–50; Middle English trecherous, from Anglo-French, equivalent to trecher “deceiver” ( trech(ier) “to deceive” + -er -er 2 ) + -ous -ous; compare French tricheur “trickster”

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Answering that question is more treacherous than usual.

From The Wall Street Journal • Apr. 1, 2026

What the pair found was a desert highway that rolls up and down, like an asphalt serpent, with deadly blind peaks and treacherous hidden troughs.

From Barron's • Mar. 8, 2026

Tuesday, setting off a challenging rescue operation in treacherous, remote, freezing conditions, eventually reaching the six survivors around 5:30 p.m.

From Los Angeles Times • Feb. 19, 2026

According to Curtis, the discovery coincides with 30 years since the Sea Empress oil spill, highlighting how "treacherous" Pembrokeshire waters can be.

From BBC • Feb. 17, 2026

I felt it necessary to change the subject, however awkwardly, as we were heading here towards treacherous waters.

From "The Secret History" by Donna Tartt

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.