六月霜

liùyuèshuāng ㄌㄧㄡˋ ㄩㄝˋ ㄕㄨㄤ

    • something that can't possibly happen
    • the impossible

Character by character

Saying俗语俗語

Idiom惯用语 · Rarely used now

Literally
frost in June
Meaning
Something that can't possibly happen. It also recalls a legend of injustice, but here it just means the impossible.

Sources