interjection, modal particle · eh; huh (used to express surprise)

欸，你怎麼在這裡？

interjection · interjection expressing sadness, regret, or a heavy heart

欸，这件事真难办。

interjection · interjection used as a response to a call or to signify agreement

欸，好，我这就来。

interjection · used in the compound 欸乃 ǎi​nǎi to describe the sound of rowing or oars creaking

煙銷日出不見人，欸乃一聲山水綠。

onomatopoeia · to sigh or to rebuke someone loudly (literary usage)

他在席間長欸一聲，似有無限感慨。

interjection · hey (used to draw attention)

欸，你看那个人是谁？

interjection · interjection used to express disapproval or surprise

欸，你怎么能这样说话呢？

interjection · yes (used to express agreement)

欸，你說得對。