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.
他公开脱离该党,并谴责了党内那些背信弃义的领导人。
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.
这条河的水流湍急而且变化莫测。