treacherous
- Hazardous or extremely dangerous conditions.
The already dangerous road on the narrow mountain pass was made even more treacherous by the high incidences of rock falls.
The hurricane resulted in treacherous weather conditions and extensive damage to property.
- Behaviour that is untruthful, deceptive or born of ill intent.
Some people think Edward Snowden did a public service when he revealed the snooping activity of the NSA, and others feel his actions were treacherous, and that he should be jailed.