一旦

• 拼音: yī dàn
• 汉字拆解: 一 = one; 旦 = 日 (sun) + 一 (horizon) — the sun rising, meaning dawn or day

含义

Once; in case; if/when (something happens). Introduces a hypothetical condition, often with significant consequences.

A formal conjunction used to express 'once X happens' or 'if X were to happen.' Often implies that the consequence is significant, irreversible, or serious. Common pattern: 一旦...就... (once...then...).

例句

1. 一旦做出决定，就不要轻易改变。
2. 一旦发现问题，请立即报告。
3. 这种机会一旦错过就不会再有了。

用法指南

语境: warning, conditional, emphasis

语气: serious

正确说法

• 一旦出了问题怎么办？(What if a problem arises?)
• 一旦成功，一切都值得。(Once successful, everything is worth it.)

错误说法

• 说'一旦我吃午饭'表示当我吃午饭时 (Don't use 一旦 for routine events — use 当...的时候; 一旦 implies significant or unusual conditions)

起源与历史

一 (one) + 旦 (dawn, day). Originally meaning 'one day' or 'some day,' evolved to mean 'once/if at some point.'

文化背景

世代: All ages

社会背景: Universal