先せん夜や

noun, adverb

the other night; a few nights ago

Refers to a recent night, typically within the past few days. Often used in narrative or explanatory contexts.

• 先せん夜や、不ふ思し議ぎな夢ゆめを見みた。

  I had a strange dream the other night.

• 先せん夜やの出で来き事ごとを詳くわしく話はなしてくれた。

  He told me in detail about the events of a few nights ago.