How common it is
一旦 appears often in everyday Chinese, so it is worth practicing early and reviewing often.
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Pronunciation focus
Say yí dàn slowly first, then repeat it in a short phrase. Listen for the tone shape.
Usage note
一旦表示如果有一天或突然发生。
Yīdàn biǎoshì rúguǒ yǒu yī tiān huò tūrán fāshēng.
Once means if one day or suddenly happens.
Context note
一旦常用于假设或条件句。
Yīdàn chángyòng yú jiǎshè huò tiáojiàn jù.
Once is often used in hypothetical or conditional sentences.
5 examples
一旦下雨，我们就回家。
yí dàn xià yǔ， wǒ men jiù huí jiā。
Once it rains, we go home.
一旦开始，就要坚持。
yí dàn kāi shǐ， jiù yào jiān chí。
Once you start, you must persist.
一旦学会，就很简单。
yí dàn xué huì， jiù hěn jiǎn dān。
Once you learn it, it's very simple.
一旦迷路，要问人。
yí dàn mí lù， yào wèn rén。
Once lost, ask someone.
一旦决定，不要后悔。
yí dàn jué dìng， bú yào hòu huǐ。
Once decided, don't regret.
5 mini stories
一旦太阳出来，雪就融化。
yí dàn tài yáng chū lái， xuě jiù róng huà。
Once the sun comes out, the snow melts.
一旦小猫长大，就会抓老鼠。
yí dàn xiǎo māo zhǎng dà， jiù huì zhuā lǎo shǔ。
Once the kitten grows up, it will catch mice.
一旦写完作业，就可以玩。
yí dàn xiě wán zuò yè， jiù kě yǐ wán。
Once homework is done, you can play.
一旦春天来了，花就开了。
yí dàn chūn tiān lái le， huā jiù kāi le。
Once spring comes, flowers bloom.
一旦学会骑车，就很有趣。
yí dàn xué huì qí chē， jiù hěn yǒu qù。
Once you learn to ride a bike, it's fun.