treacherous

Meanings

1. 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. 2
   adj

   Likely to betray someone's trust; not loyal.

   His treacherous friend secretly told their rivals about the plan.

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

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