This is the 86th most frequent Vietnamese word.
khi
The Vietnamese word "khi" can mean "when," "while," or "gas/air," depending on context.
This sentence uses "khi" as a conjunction meaning "when" to indicate the time at which the action occurs.
Tôi học bài khi mặt trời lặn.
I study lessons when the sun sets.
Here, "khi" is also acting as a conjunction meaning "when," referring to a point in time of an event.
Hãy báo tôi biết khi bạn đến.
Let me know when you arrive.
In this example, "khi" continues to function as a conjunction for "when," setting a conditional framework for the statement.