1. deliberately betraying trust or a promise; disloyal and treacherous

背信弃义的；不忠的；阴险狡诈的

The perfidious ally secretly signed a treaty with our rival behind our backs.

那个背信弃义的盟友背地里和我们的对手签订了协议。

拉丁语词根 perfidus：per-（彻底、穿透）+ fid（信任、忠诚，faith 同源）+ -ious 形容词后缀

字面本意：彻底背弃信义的

联想：完全击穿彼此的信任 → 背叛、不忠

Historians described the ruler as perfidious for breaking every peace agreement he had made.

历史学家称这位统治者背信弃义，所有和平协议均被他撕毁。

perfidious traitor 阴险叛徒

perfidious scheme 阴险诡计

perfidious behaviour 背信弃义的行径

Don’t trust him, he’s super perfidious and will stab you in the back anytime.

别信他，这人特别阴险，随时会背后捅你一刀。

It’s so perfidious of her to leak our plan to competitors for petty gains.

她为一点小好处就把方案泄露给对手，实在太不讲信义了。