照妖鏡

Simplified: 照妖镜

zhàoyāojìng ㄓㄠˋ ㄧㄠ ㄐㄧㄥˋ

    • magic mirror for revealing goblins
    • fig. way of seeing through a conspiracy

Character by character

Saying俗语俗語

Idiom惯用语 · Widely known

Literally
demon-revealing mirror
Meaning
A thing that exposes the true nature of bad people. It comes from the magic mirror in myths that shows demons in their real form.

Sources