How to say "eve" in Japanese

• 前日ぜんじつCommon
  noun, adverbRefers to the day before an event as a whole — the previous day itself, not the evening. Use it when 'eve' means 'the day before', as with the day before an exam or ceremony.
  私はその前日ぜんじつ彼かれにあった。↗

  I met him on the previous day.
• イブCommon
  nounA borrowing of English 'eve': it means Christmas Eve above all, and can also refer to the night before an occasion. If your 'eve' is Christmas Eve, this is the word to reach for.
  街まちはクリスマスムード一色いっしょく・・・もうじきイブだ。↗

  The streets are in full Christmas mood - it's almost Christmas Eve.
• 前夜祭ぜんやさいCommon
  nounNot 'eve' as a time; it names an event — a festival or party held the night before another event. It fits only when 'eve' refers to that celebration itself, as with Christmas Eve festivities.
• 前夜ぜんやCommon
  noun, adverbThe night before Christmas, a festival, or another major event; choose it when 'eve' refers to the night itself rather than the whole previous day.
  まるで革命かくめい前夜ぜんやのような騒さわぎだった。↗

  It looked as if we were on the eve of a revolution.

前日 is the day before an event, 前夜 the night before a major one, 「イブ」 the night before especially Christmas Eve, and 前夜祭 an event held on such a night rather than the eve itself.

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

• 前日ぜんじつprevious day
• イブeve (esp. Christmas Eve)
• 前夜祭ぜんやさいevent held the night before another event
• 前夜ぜんやnight before (Christmas, etc.)