treacherously
gb/tɹˈit͡ʃɚˈɔsli/ us/tɹˈit͡ʃɚˈɔsli/
C1
English
Senses
0 senses
adverb
formal
C1
property
1
in a disloyal, betraying way
in a way that is not loyal and hurts someone’s trust
Usage pattern:
[someone] acts/speaks treacherously (toward/against [someone])
Common mistake:
Do not confuse with 'dangerously' (physical risk). 'Treacherously' often suggests betrayal or deliberate deceit.
Synonyms
deceitfully (emphasizes lying or tricking rather than betrayal of loyalty.)
|
betrayingly (more directly highlights the idea of betrayal.)
|
faithlessly (stresses lack of loyalty or commitment.)
Antonyms
loyally (shows faithful support rather than betrayal.)
|
faithfully (emphasizes keeping trust and commitments.)
|
honorably (stresses acting by ethical principles rather than deceit.)
Collocations
act treacherously
|behave treacherously
|deal treacherously with
|treacherously betray
|treacherously undermine
|treacherously turn on someone
|treacherously plot against
|treacherously deceive
Themes
relationships
|ethics
|conflict
Examples
- He treacherously fed information to their competitors while pretending to support the team.
- She smiled politely, then treacherously repeated his private comments to the boss.
- They were accused of treacherously abandoning their allies at the last moment.
Learner examples
- He acted treacherously and betrayed his friend.
- She spoke treacherously to gain power.
adverb
C1
property
2
in a dangerously unsafe way
in a way that is very dangerous and not safe
Usage pattern:
[place/thing] is treacherously [adjective] / [something] becomes treacherously [adjective]
Common mistake:
Learners may overuse 'treacherously' for any danger. It often implies hidden or unexpected danger (e.g., ice, currents, a narrow path).
Synonyms
dangerously (more general; lacks the sense of hidden or tricky danger.)
|
perilously (often suggests closeness to disaster or extreme risk.)
|
hazardously (more technical and safety-focused.)
Antonyms
safely (indicates absence of danger.)
|
securely (stresses stability and protection from harm.)
Collocations
treacherously slippery
|treacherously icy
|treacherously steep
|treacherously narrow
|treacherously rough
|treacherously strong currents
|treacherously fast water
|treacherously unstable ground
Themes
travel
|weather
|safety
|nature
Examples
- The sidewalk was treacherously icy after the overnight freeze.
- The trail turns treacherously steep near the summit, especially in wet weather.
- The sea looked calm, but the current ran treacherously fast along the rocks.
Learner examples
- The road was treacherously slippery.
- The river was treacherously strong.
adverb
literary
C2
property
3
deceptively safe or simple
in a way that looks safe or easy but is not
Usage pattern:
treacherously + [adjective] (e.g., calm, simple, quiet)
Common mistake:
This use is close to 'deceptively'. It usually implies that the hidden problem could cause harm or failure.
Synonyms
deceptively (neutral about why it misleads; 'treacherously' adds a sense of danger.)
|
misleadingly (focuses on incorrect impressions, not necessarily danger.)
Antonyms
openly (not hidden or deceptive.)
|
straightforwardly (clearly and without hidden difficulty.)
Collocations
treacherously calm
|treacherously quiet
|treacherously simple
|treacherously smooth
|treacherously easy
|treacherously inviting
Themes
risk
|communication
|daily_life
Examples
- The first chapter is treacherously simple, but the problems get complex fast.
- The lake was treacherously calm, hiding the sharp rocks just under the surface.
- His question sounded treacherously friendly, as if it were designed to trap her.
Learner examples
- The test looked treacherously easy.
- The water was treacherously calm.
Grammar
Dictionary form
treacherously
IPA
GB/tɹˈit͡ʃɚˈɔsli/
US/tɹˈit͡ʃɚˈɔsli/
Syllables & stress
treach - er - ously (3 syllables)
Stress on 1st syllable (treach)
Word forms
Noun
- Base: treacherously
- Plural: treacherouslies
Expressions
treacherously close (to)
1/tɹˈit͡ʃɚˈɔsli klˈoʊs tə/
fixed phrase
uncomfortably near a danger
very close to something dangerous or bad
Examples
- By midnight, the fire was treacherously close to the nearest homes.
- Without new funding, the project is treacherously close to collapse.
- One mistake and they would be treacherously close to open conflict.