1) ADJ-GRADED If you describe someone as treacherous, you mean that they are likely to betray you and cannot be trusted.

He publicly left the party and denounced its treacherous leaders...

The President spoke of the treacherous intentions of the enemy.

2) ADJ-GRADED If you say that something is treacherous, you mean that it is very dangerous and unpredictable.

The current of the river is fast flowing and treacherous...

They made the treacherous journey across stormy seas in rotten boats.

English dictionary. 2008.