How to say "brood" in Japanese

• 考え込むかんがえこむCommon
  godan verb, intransitive verbCovers brooding in the sense of pondering: thinking long and hard about a problem or decision. The emphasis falls on deep, sustained thought, as when someone sits lost in thought over a difficult choice.
  彼かれは心配しんぱい事ことを考かんがえこんで、一いち日にち中ちゅう座すわっていた。↗

  He sat brooding over his troubles all day.
• くよくよCommon
  suru verbCovers brooding as fretting or moping: dwelling unhappily on something that weighs on the mind. Its mimetic character lends an emotional, dispirited flavor, as of someone unable to stop worrying over a setback.

For brooding as deep, sustained pondering, use 「考え込む」; for brooding as fretting or moping over troubles, use 「くよくよ」, whose mimetic character adds a flavor of worry and low spirits.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 考え込むかんがえこむto ponder
• くよくよto fret (over)
• 繁殖用はんしょくようbrood
• ふさぎ込むふさぎこむto mope
• 抱くだくto sit on (eggs)