秘而不宣 (mì ér bù xuān) | Meaning: to withhold information | Chinese Idiom with Pinyin & Origin

lit. to guard one's mouth like a closed bottle (idiom); tight-lipped · reticent · not breathing a word守口如瓶shǒu kǒu rú píng

in the dark · in secret · on the sly · surreptitiously暗中àn zhōng

a hidden trouble hard to mention (idiom) · sth too embarrassing to mention · an embarrassing illness难言之隐nán yán zhī yǐn

(idiom) to steadfastly refuse to discuss the matter; to treat it as an untouchable subject讳莫如深huì mò rú shēn

to withhold information · to keep sth secret