一旦 (yídàn) – once, as soon as (if ever)

Pattern

• 一旦 + Condition，（Subject）+ 就 + Result

Usage

• Opens the first clause to suppose “if this should ever happen”, leading to the result in the second clause with 就; the result is often serious or hard to undo.

Examples

1. 1

   一旦有人闯入这个空间，我们就会感觉不舒服、不自在。

   Yídàn yǒu rén chuǎngrù zhège kōngjiān, wǒmen jiù huì gǎnjué bù shūfu, bú zìzài.

   Once someone intrudes into this space, we feel uncomfortable and ill at ease.

2. 2

   机会一旦错过，就不会再来。

   Jīhuì yídàn cuòguò, jiù bú huì zài lái.

   Once an opportunity is missed, it won't come again.