verb · to heave a sigh of sadness, regret, or weariness

他深深地唉了一口气，显得非常忧郁。

interjection · interjection or grunt of agreement or recognition

唉，我这就来。

interjection · an interjection used to express sadness, disappointment, or a sigh of regret

唉，真可惜，我们还是输了。