How to say "thoroughly" in Japanese

• じっくりJLPT N1approx.Common
  adverb (with と)Doing something thoroughly in the sense of slowly and carefully, without haste—taking your time over it. Use it for savoring, considering, or working through something attentively rather than for completeness as a result.
  じっくり彼かれに耳みみを貸かす者ものはいない。↗

  No one stops to listen to him.
• 散々さんざんCommon
  na-adjective, adverbThoroughly in the sense of utterly or to an exhausting degree, usually with a negative outcome—being thoroughly scolded, lost, or worn out. It implies the experience went far enough to be unpleasant.
• すっかりJLPT N4approx.Common
  adverb (with と)Thoroughly as in completely or entirely—a state that has wholly changed or been finished. It describes the resulting completeness, not the manner of doing something, so it suits forgetting, changing, or being convinced.
  私はすっかり息いきが切きれた。↗

  I am completely out of breath.
• 片っ端からかたっぱしからCommon
  adverbThoroughly in the sense of systematically dealing with absolutely everything, one item after another without skipping any. Use it when the thoroughness lies in covering every single thing from start to finish.
• 思う存分おもうぞんぶんCommon
  expression, adverbDoing something thoroughly in the sense of to your heart's content or as much as you like—enjoying it fully without holding back. It expresses personal satisfaction, not completeness of a task, so it is a looser match for 'thoroughly'.
  その独裁者どくさいしゃは思おもう存分ぞんぶん特権とっけんを乱用らんようした。↗

  The dictator abused his privileges to his heart's content.

「thoroughly」 covers several ideas: careful unhurried doing, exhausting or suffering through something, complete change of state, doing every item in order, and doing something as much as you like—pick by which of these you mean.

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

• じっくり(slowly and) carefully
• 散々さんざんthoroughly
• すっかりall
• 片っ端からかたっぱしからabsolutely every little bit
• 思う存分おもうぞんぶんto one's heart's content
• 根掘り葉掘りねほりはほりinquisitively
• とっくりthoroughly
• さんざっぱらthoroughly
• 徹頭徹尾てっとうてつびthoroughly
• さんざんぱらthoroughly
• とくとcarefully
• すっぱりcompletely (quitting, etc.)
• こてんぱんcompletely (beaten, defeated, etc.)
• 完膚なきまでかんぷなきまでcompletely
• 余すところなくあますところなくfully
• まんべんなくequally
• しらみつぶしにone by one
• 端から端まではしからはしまでfrom one end to another
• すぱっとcompletely (quitting, etc.)
• こてんこてんcompletely (beaten, defeated, etc.)
• 余すことなくあますことなくfully
• まんまとsuccessfully
• 片端からかたはしからabsolutely every little bit
• とことんまでto the very end
• ためつすがめつ(scrutinizing) carefully
• 十分じゅうぶんsufficiently
• ばっちりenough
• とことんto the very end
• すっくりall
• ばっちしenough
• 根こそぎねこそぎall (destroyed, stolen, etc.)
• すっきりcompletely
• どこまでもthoroughly