adj
treacherous
TREHT-shuh-ruhs
adj
1
Willing to betray trust; disloyal and deceitful.
"His treacherous business partner sold the company's secrets to a rival."
2
Dangerous or unreliable, especially in a way that isn't obvious at first.
"The icy mountain road was treacherous after dark."
How to Use Treacherous
Learner’s notesIn plain EnglishTreacherous describes either a person who betrays trust or a situation/place that's secretly dangerous.
Common pairings
treacherous conditions
treacherous waters
a treacherous friend
Word Forms
more treacherous comparative, most treacherous superlative
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His _____ business partner sold the company's secrets to a rival.
Etymology
From Old French trecheros, "deceitful" — related to "treachery."