The origins of なんだ as in 飲まなんだ　or せなんだ


Even here in Osaka I don't hear it very often among anyone even remotely
young, but where does this come from originally? Does anyone have a reference
on hand?

If I myself had to guess from what I know of classical Japanese I would think
it could be

（打ち消し）ぬ → （連用形）に + あり + たり → にありたり → にありた → なりた → なんだ

Thanks.




According to a dictionary,

> この語の成立については未詳。一説に「ぬあった」の転かともいう

[source](http://kotobank.jp/word/%E3%81%AA%E3%82%93%E3%81%A0)

