Indicates doing something as a temporary measure or a single action before a later change; often used with ～したら or ～してから.
I'll go home once and then go out again.
一旦決めたことは、最後までやり通そう。
Once you've decided something, see it through to the end.
for a short time; briefly; temporarily
Describes a temporary state or pause; often used with verbs like 止める, 中断する, or 落ち着く.
雨が強くなったので、一旦作業を中断した。
The rain got heavier, so we temporarily stopped work.
一旦落ち着いて、状況を確認しましょう。
Let's calm down for a moment and check the situation.
one morning
Archaic noun meaning 'one morning'; not used in modern Japanese outside of classical texts.
古文では「一旦」を「ある朝」の意味で使うことがある。
In classical Japanese, 一旦 can be used to mean 'one morning'.
Once you decide, you should see it through to the end.
He paused for a moment to reconsider.
I'll go back home for a bit and then start over.
We decided to temporarily suspend the meeting.