いったん・一旦ittan[0]heiban (flat)

1. adverbonce
   いったんしたことは元もとどおりにならない。↗

   What is done cannot be undone.
2. adverbfor a short time; briefly; temporarily
   いったん着地ちゃくちした怪物かいぶつは、瞬間しゅんかんふたたび跳躍ちょうやくして私の頭上ずじょうにいた。↗

   Having once landed the monster immediately jumped again and was over my head.
3. nounone morning

• RelatedひとまずNeutralNeutral: 'for now, tentatively', as in 「ひとまず安心」 — a matter is brought to a temporary close. 「一旦」 also has a conditional 'once…' use, as in 「一旦〜すると」.
• RelatedとりあえずCasualCommon in speech: 'first, for now', as in 「とりあえずビール」. It stresses a stopgap move for the moment, unlike 「一旦」, which covers temporary halts and conditionals.

Use 「一旦」 for a temporary pause, or in conditionals such as 「一旦〜すると」 ('once you…, then…'). Use 「ひとまず」 to settle a matter for now; colloquial 「とりあえず」 is for a stopgap 'first, for now'.

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

1. （仮定かてい的てき表現ひょうげん・条件じょうけんの成就じょうじゅ的てき表現ひょうげんに先立さきだって）一度いちど。
2. （他たに先駆さきがけ）ひとまず。