An interjection expressing surprise, disbelief, or asking someone to repeat something ("Eh?"/"What?").
えっ、本当に明日帰国するの？
Eh? You're really going back home tomorrow?
A: 明日の会議は中止だって。 B: えっ、聞いてないよ。
A: Tomorrow's meeting is canceled. B: Eh? I didn't hear that.
えっ…そんなことが起こるなんて信じられない。
Eh... I can't believe something like that happened.
えっ？もう終電がないの？早く帰ろう。
What? There's no last train left? Let's hurry home.