1.
once; if/when once; the moment that
A literary adverb meaning 'once' in the sense of 'once (something happens)' — used in conditional or temporal clauses to set up a consequence that follows from a single occurrence. Has a written, formal tone.
一度決めたら変えない。
Once I decide, I don't change my mind.
一度戦争が始まれば、多くの命が失われる。
Once war begins, many lives are lost.
一度信頼を失えば、それを取り戻すのは容易ではない。
Once you lose someone's trust, regaining it is no easy task.
An alternate, literary reading of 一度. Where いちど means 'one time' in counting terms, ひとたび is always adverbial and conditional in flavor — 'once X happens, then Y'.
TYPICAL PATTERNS:
- 一度…ば / たら: once… (if/when once)
- 一度…と: the moment (something happens)
REGISTER: Strongly literary. Common in essays, speeches, and proverb-like statements; uncommon in casual conversation, where the spoken equivalent would be ⌜一度…たら⌟ or ⌜いったん…たら⌟.
SIMILAR WORDS:
- 一度: once, one time — neutral, can be a literal count
- いったん: once, for the moment — closer to ひとたび in the conditional sense, more conversational
- 一たび: mixed kana form occasionally seen in older writing