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
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.
New Zealander Woods and her team battled two heatwaves, storms, a swarm of horseflies, and wildfires that resulted in a detour that added five kilometres and 200m of treacherous climbing to her route.
From BBC ● Aug. 2, 2026
Ceuta's regional president said at least 34 people have lost their lives in the treacherous dash into the territory.
From Barron's ● Jul. 31, 2026
Software exposure had been the thing for investors to avoid after a treacherous start to the year.
From MarketWatch ● Jul. 21, 2026
“It turned out losing my voice was not too treacherous for me,” she told the Guardian.
From Los Angeles Times ● Jul. 9, 2026
And given the present setting—a dark, treacherous bend of blacktop—it was pretty easy to come up with something good.
From "Anthem of a Reluctant Prophet" by Joanne Proulx
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.
