Dic: treacherous

• He publicly left the party and denounced its treacherous leaders.
• He was cruel, treacherous, and unscrupulous.
• The current of the river is fast flowing and treacherous.
• The tides here can be very treacherous.

ADJ | If you describe someone as treacherous, you mean that they are likely to betray you and cannot be trusted. | disloyal and untrustworthy.

1. Marked by betrayal of fidelity, confidence, or trust; perfidious. See Synonyms at faithless.
2. Not to be relied on; not dependable or trustworthy.

ADJ | If you say that something is treacherous, you mean that it is very dangerous and unpredictable. | unreliable or dangerous, esp. because of sudden changes. | Marked by unforeseen hazards; dangerous or deceptive.

.... Cobuild, Collins Essential, The American Heritage