How to say "unprecedented" in Japanese

• 破格はかくCommon
  no-adjective, na-adjectiveReally means extraordinary or exceptional, often of exceptionally favorable prices, terms, or treatment; its link to 'unprecedented' is only that exceptional sense, so it is seldom the word you want for 'never done before'.
• 空前くうぜんCommon
  no-adjectiveCovers 'unprecedented' in the sense of record-breaking scale: a success, crowd, or boom the like of which has never been seen. It stresses magnitude rather than mere novelty.
  これは空前くうぜんの大事件だいじけんとして歴史れきしに残のこるでしょう。↗

  This will go down in history as the greatest event that has ever taken place.
• 破天荒はてんこうCommon
  na-adjective, nounCovers 'unprecedented' as unheard-of audacity: conduct or achievements so unconventional they defy ordinary expectations. Best fits daring, unconventional people and exploits rather than record-breaking events or statistics.
• 画期的かっきてきCommon
  na-adjectiveCovers 'unprecedented' in the sense of groundbreaking or revolutionary: a method, product, or idea that breaks new ground and changes how things are done, rather than an event without historical parallel.
• 前代未聞ぜんだいみもんCommon
  no-adjectiveA four-character idiom presenting an event as unparalleled in history — never before heard of; it often carries a tone of astonishment, whether the event is an achievement or a scandal.
  犯人はんにんを弁護べんごしてた弁護士べんごしが実じつは真犯人しんはんにんだったなんて、前代未聞ぜんだいみもんだ。↗

  It's totally without precedent for the suspect's attorney to be the true culprit.

Choose 空前 for unprecedented scale, 前代未聞 for events unparalleled in history, 画期的 for groundbreaking innovation, 破天荒 for audacious unconventionality, and reserve 破格 for exceptional terms or treatment rather than historical firsts.

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

• 破格はかくextraordinary
• 空前くうぜんunprecedented
• 破天荒はてんこうunheard-of
• 画期的かっきてきground-breaking
• 前代未聞ぜんだいみもんunheard-of
• 前人未到ぜんじんみとうuntrodden (region, field of study, etc.)
• 異例いれいexceptional
• 未曾有みぞうunprecedented
• 事新しいことあたらしいunprecedented
• 類のないるいのないunprecedented
• 前人未発ぜんじんみはつunprecedented
• 類を見ないるいをみないunprecedented
• かつてないunprecedented
• 今までにないいままでにないunprecedented
• 曠古こうこhistoric
• 神武以来じんむこのかたsince the era of the Emperor Jimmu
• 未到みとうunreached
• 比類のないひるいのないunparalleled