冥思苦索

míngsīkǔsuǒ
  1. to mull over (idiom)
  2. to think long and hard

CEDICT

to think long and hard; to rack one's brains; to cudgel one's brains

Wiktionary

形容動腦筋，反覆思考。如：「為了這次勞資糾紛問題，他冥思苦索了好幾天，希望能有一個兩全其美的好方法。」也作「冥思苦想」。

重編國語辭典

絞盡腦汁，反覆思考

維基詞典

Entry Composition

1 冥思 míngsī
  1. (literary) delusion; fantasy
  2. delusion; fantasy
  3. to think hard; to cudgel one's brains
2 苦 kǔ
  1. bitter
  2. hardship
  3. pain
  4. to suffer
  5. to bring suffering to
  6. painstakingly
3 索 suǒ
  1. to search
  2. to demand
  3. to ask
  4. to exact
  5. large rope
  6. isolated

Related entries

琢磨 zuómo
  1. to ponder
  2. to mull over
  3. to think through
  4. Taiwan pr. zhuómó
醞釀 yùnniàng
  1. (of alcohol) to ferment
  2. (of a crisis) to be brewing
  3. to mull over (an issue)
  4. to hold exploratory discussions
他们的友情酝酿成爱情的果实。

Their friendship ripened into a deep love.

Source: Tatoeba

咂摸 zāmo
  1. (dialect) to savor
  2. to test the taste of
  3. (fig.) to ponder upon
  4. to mull over
咬嚼 yǎojiáo
  1. to chew
  2. to masticate
  3. to ruminate
  4. to mull over