treacherous
Americanadjective
-
characterized by faithlessness or readiness to betray trust; traitorous.
- Synonyms:
- treasonous, faithless, unfaithful
- Antonyms:
- loyal
-
deceptive, untrustworthy, or unreliable.
- Synonyms:
- deceitful
- Antonyms:
- reliable
-
unstable or insecure, as footing.
-
a treacherous climb.
adjective
-
betraying or likely to betray faith or confidence
-
unstable, unreliable, or dangerous
treacherous weather
treacherous ground
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”
Explanation
Treacherous means either not trusted or dangerous. A treacherous road might be icy or otherwise likely to cause a car accident. A treacherous friend will betray you. Treachery refers to harmful acts you might do to someone who trusts you. It can also refer to being disloyal to your native country, but the word treason is more common in this sense. Treachery is from Middle English trecherie, from Old French, from trichier "to trick or cheat." The English word trick is from trikier, a slightly different spelling that was used in some dialects of Old French.
Vocabulary lists containing treacherous
List 2
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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.
He has investigated the agendas of powerful fossil fuel billionaires, delved into epic feuds pitting some of the world's largest energy companies against each other, and revealed how drillers navigate a treacherous political landscape.
From The Wall Street Journal • Mar. 2, 2026
A 70-year-old man died Tuesday after falling from a cliff along California’s treacherous Devil’s Slide, an oceanside stretch in Pacifica known for steep terrain that has led to several fatal accidents.
From Los Angeles Times • Feb. 25, 2026
“Sharply reduced visibility will make travel extremely treacherous across these areas.”
From Barron's • Feb. 22, 2026
Conditions on Wednesday remained dangerous, multiple officials said, with Woo describing the climate as "treacherous".
From BBC • Feb. 18, 2026
“Are you sure she is safe?” whispered Jo, looking remorsefully at the golden head, which might have been swept away from her sight forever under the treacherous ice.
From "Little Women" by Louisa May Alcott
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.
