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
Looking to grow your vocabulary? Check out this interactive, curated word list from our team of English language specialists at Vocabulary.com – one of over 17,000 lists we've built to help learners worldwide!
ASVAB Word Knowledge
Interested in learning more words like this one? Our team at Vocabulary.com has got you covered! You can review flashcards, quiz yourself, practice spelling, and more – and it's all completely free to use!
Unit 1: Telling Details
Want to remember this word for good? Start your learning journey today with our library of interactive, themed word lists built by the experts at Vocabulary.com – we'll help you make the most of your study time!
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.
Several trekkers and their guides say their journeys back down the mountains have been treacherous, taking up to three or four days and requiring them to pass collapsed roads and swept-away bridges.
From BBC ● Sep. 30, 2026
Nepal's mountain districts have seen persistent rain and snow in recent days, creating treacherous conditions for the country's economically important climbing tourism industry.
From BBC ● Sep. 27, 2026
So is Adeline Rudolph as Renee Birdwhistle, the secretary at Neagley’s detective agency and budding sleuth who rises to each treacherous occasion with remarkable—some might say unbelievable—skill.
From The Wall Street Journal ● Sep. 15, 2026
Nepali rescue teams battled difficult terrain, an unpredictable river and treacherous marshland on Monday, the sixth day in their search for survivors and victims of devastating floods.
From Barron's ● Aug. 31, 2026
Nations such as Russia, Poland, and Finland also experienced disastrous economic times and suffered from oppressive governments, leading many to risk the long, treacherous ocean voyage to America.
From "1919 The Year That Changed America" by Martin W. Sandler
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.
