in a single day; in a very short time; in case [something happens] (adv.)
HSK 5
Traditional
一旦 (unaltered)
Radicals
Stroke order
Examples
一旦你开始，就不要停下来。 yīdàn nǐ kāishǐ, jiù bùyào tíng xiàlái。 - Once you start, do not stop.
一旦你做出决定，就要坚持下去。 yīdàn nǐ zuòchū juédìng, jiù yào jiānchí xiàqù。 - Once you make a decision, stick to it.
一旦发生火灾，请立即报警。 yīdàn fāshēng huǒzāi, qǐng lìjí bào jǐng。 - In case of fire, please call the police immediately.
一旦丢失了这个文件，就无法恢复。 yīdàn diūshīle zhège wénjiàn, jiù wúfǎ huīfù。 - Once this document is lost, it cannot be recovered.
一旦开始下雨，河流就会迅速涨水。 yīdàn kāishǐ xià yǔ, héliú jiù huì xùnsù zhǎng shuǐ。 - Once it starts to rain, the river will rise quickly.
Characters
一 yī - one; once; first; structural word between two of the same verb; as soon as; throughout | HSK 1
旦 dàn - dawn, daybreak; day |