what?!; what did you say?!
An exclamation of surprise or disbelief, often used when hearing unexpected news. Casual and conversational.
え、なんだって？もう一度言って。
Huh, what?! Say that again.
彼が辞めるって？なんだって！
He's quitting? What?!
why?; what for?
Used to ask the reason for something, often with a tone of surprise or demand. More emphatic than なぜ.
なんだってそんなことしたの？
Why on earth did you do that?
なんだって今頃
Used in the pattern なんだって～ to mean 'anyone' or 'anything', similar to 何でも. Often followed by a verb like できる or いい.
See also: なんでも
彼はなんだってできる。
He can do anything.
What are you doing here at this hour?
なんだっていいよ。
Anything is fine.
Contraction of 何と (なんと) and 言って (いって), literally 'what did you say?'. The adverbial uses developed from this interrogative origin.