殫精竭慮 [殚－－虑]

Jyutping daan1 zing1 kit3 leoi6
Pinyin dān jīng jié lǜ

Definitions (CC-CEDICT)
  1. to exhaust one's thoughts and ingenuity (idiom); to think sth through thoroughly
  2. to rack one's brains
  3. to leave no stone unturned
Definitions (Wiktionary)
  1. phrase, idiomatic
    to exhaust one's energy and rack one's brain
Definitions (Kaifangcidian)
  1. （沒有對應漢語詞彙）