海底撈月（かいていろうげつ）

Japanese vocabulary

Meaning: totally useless (fruitless) effort; wasting time on an impossible task (like trying to scoop up a reflected moon from the bottom of the sea)

Etymology

Loanword from Chinese “hǎidǐ-lāoyuè”.

See it used in real works

• Example sentences from Japanese novels & web fiction (Massif)
• Hear “海底撈月” pronounced in real videos (YouGlish)