一いっ昨さく夜や

noun, adverb

the night before last

Refers to the night two nights ago. Used as a noun or adverb. More formal than おとといの夜.

• 一いっ昨さく夜やはよく眠ねむれなかった。

  I couldn't sleep well the night before last.

• 一いっ昨さく夜やの出で来き事ごとを覚おぼえていますか。

  Do you remember what happened the night before last?