treacherous

C2 Topic:Describing Qualities

US /ˈtɹɛt͡ʃəɹəs/ See IPA manual

Freq #11075

Meanings

1

adj
Dangerous and unpredictable, especially because hidden hazards are hard to see.

The icy roads were treacherous, and several cars slid off into ditches.
2

adj
Likely to betray someone's trust; not loyal.

His treacherous friend secretly told their rivals about the plan.

Thesaurus

Synonyms

1 adj · dangerous and... dangerous hazardous perilous unsafe

2 adj · likely to betray someone's... deceitful perfidious traitorous

More booky dastardlydislealdisloyaldouble-crossingdouble-dealingdouble-faceddouble-hearteddoubleheartedfaithless falsefalse-hearted

Opposites

faithfulfidelitouslealloyal steadfast trueuntraitorousuntreacherous

Word family

Related forms betray betrayal betrayer treacher treachery trick trickster tricky

Appears in

Phrases (1)

See all

most treacherous
more likely than others to betray trust or act disloyally

Adverb + adjective

Etymology

From Old French trecheros, tricheros (“deceitful”), equivalent to treacher + -ous. See treacher.

trecheros Old French

View etymology graph ->

Topics

Describing Qualities Word Formation & Derivatives

External links

# treacherous

**Type:** Word
**Level:** C2
**Part of speech:** adj
**IPA (US):** /ˈtɹɛt͡ʃəɹəs/
**Frequency rank:** 11075

## Meanings
1. Dangerous and unpredictable, especially because hidden hazards are hard to see.
2. Likely to betray someone's trust; not loyal.

## Examples
- The icy roads were treacherous, and several cars slid off into ditches.
- His treacherous friend secretly told their rivals about the plan.

## Synonyms
- booky
- dastardly
- disleal
- disloyal
- double-crossing
- double-dealing
- double-faced
- double-hearted
- doublehearted
- faithless
- false
- false-hearted

## Antonyms
- faithful
- fidelitous
- leal
- loyal
- steadfast
- true
- untraitorous
- untreacherous

## Related Forms
- betray
- betrayal
- betrayer
- treacher
- treachery
- trick
- trickster
- tricky

## Roots and Affixes
- Root: trecheros

## Etymology
From Old French trecheros, tricheros (“deceitful”), equivalent to treacher + -ous. See treacher.

## AI Etymology
Treacherous is from Old French trecheros, tricheros (“deceitful”), equivalent to treacher + -ous. See treacher. The analysis is mainly morphological: the modern adjectival form is built from the named base and affix. Important recorded forms include trecheros (Old French). Current senses include dangerous and unpredictable, especially because hidden hazards are hard to see and likely to betray someone's trust; not loyal. The wider family includes related words such as betray, betrayal, betrayer, and treacher.

## Topics
- Describing Qualities
- Word Formation & Derivatives

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