神不知鬼不觉

Traditional (Taiwan): 神不知鬼不覺

shénbùzhīguǐbùjué ㄕㄣˊ ㄅㄨˋ ㄓ ㄍㄨㄟˇ ㄅㄨˋ ㄐㄩㄝˊ

    • top secret
    • hush-hush

Character by character

Saying俗语俗語

Idiom惯用语 · In everyday use

Literally
neither gods nor ghosts know
Meaning
Done so secretly that nobody notices. Often about sneaky or illicit actions.

Sources