一旦

yīdàn

conjunction HSK 5 #1,028

Meanings

Literally 'one dawn' — from the moment something happens

Yīdàn juédìng le, jiù bú yào hòuhuǐ.

Once you've decided, don't regret it.

Yīdàn fāshēng huǒzāi, qǐng lìjí líkāi dàlóu.

In case of fire, please leave the building immediately.

Yīdàn nǐ kāishǐ xuéxí, jiù huì fāxiàn Zhōngwén hěn yǒuqù.

Once you start learning, you'll find Chinese is very interesting.

grammar

一旦...就... is a fixed pattern meaning 'once... then...'. The 就 part describes the consequence.

usage

一旦 often implies something irreversible or something with significant consequences. It's more dramatic than 如果 (rúguǒ, if).

一 yī

旦 dàn