Translation guide
The English word "once" has several distinct uses: as an adverb meaning "one time," as a conjunction meaning "as soon as" or "after," and in phrases like "at once" (immediately) or "once upon a time." This guide covers natural Japanese equivalents for each meaning.
Expressing that something happens a single time, or happened one time in the past.
The most common and neutral way to say 'once' meaning 'one time.' Can be used in most contexts.
私は一度だけ日本に行ったことがあります。
I have been to Japan only once.
この薬は一日に一度飲んでください。
Please take this medicine once a day.
Means 'once' or 'one time,' often used when counting occurrences or turns. Slightly more casual than 一度.
週に一回ジムに行っています。
I go to the gym once a week.
Means 'once' but is more colloquial and often used in spoken Japanese. Can sound a bit rough or dialectal.
一遍やってみて。
Try it once.
Indicating that one action happens immediately after another.
The most common conditional form used to mean 'once' or 'when' in the sense of 'after something happens.' Attach to the past plain form of the verb.
家に着いたら電話します。
Once I get home, I'll call you.
宿題が終わったら遊びに行けるよ。
Once you finish your homework, you can go play.
Literally 'after doing V.' More explicit than たら, but slightly less natural for immediate sequences.
ご飯を食べたあとで散歩しましょう。
Once we've eaten, let's take a walk.
Used for 'once something happens, it leads to a certain result,' often with a nuance of irreversibility or a clear consequence.
いったん雨が降り出すと、川が増水する。
Once it starts raining, the river swells.
Expressing that something should be done right away.
The most common way to say 'immediately' or 'at once.'
すぐに来てください。
Please come at once.
More formal and urgent than すぐに. Often used in official announcements or instructions.
Can mean 'at once' in the sense of 'all at the same time' or 'simultaneously,' not necessarily 'immediately.'
Do not use 一度に to mean 'immediately.' It means 'all at once' or 'at the same time.'
The traditional fairy-tale opening.
The standard Japanese equivalent of 'once upon a time.' Used at the beginning of folk tales and children's stories.
昔々、あるところにおじいさんとおばあさんがいました。
Once upon a time, there lived an old man and an old woman.
Referring to a past state or condition that is no longer true.
Means 'once' in the sense of 'formerly' or 'at one time.' Often used in written or formal contexts.
彼はかつて有名な歌手だった。
He was once a famous singer.
Literally 'previously,' used to contrast past and present. More conversational than かつて.
以前はここに映画館があった。
There was once a movie theater here.
Means 'at one time' or 'for a period,' implying a temporary state.
一時はプロを目指していた。
I once aimed to be a professional.
Doing something decisively so it doesn't need to be repeated.
Literally 'making this the last time.' A natural way to express finality.
これを最後にタバコをやめる。
I'm quitting smoking once and for all.
An adverb meaning 'decisively' or 'once and for all.' Often used with verbs like やめる (quit) or 断る (refuse).
きっぱりとお酒をやめた。
I quit drinking once and for all.
Both mean 'once' or 'one time,' but 一度 is slightly more formal and common in set phrases like もう一度 (once more). 一回 is more casual and often used when counting specific instances. In many situations they are interchangeable.
もう一度言ってください。
Please say it once more.
もう一回言って。
Say it one more time. (casual)
When counting occurrences, Japanese uses counter words. 'Once' as a frequency is 一回 (いっかい) or 一度 (いちど). Do not use 一つ (ひとつ) which means 'one thing.'
一度だけ行ったことがあります。
I've only been there once.
始めたら止められない。
Once you start, you can't stop.
すぐに来なさい！
Come here at once!
直ちに避難してください。
Evacuate at once.
一度に全部食べないで。
Don't eat everything at once.