先せん口くち

noun

previous engagement; prior commitment

Refers to a prior arrangement or obligation that prevents one from accepting a new invitation or task. The gloss 'previous preconception' is likely a misinterpretation; the core meaning is a prior engagement. Rare and somewhat dated; modern Japanese more often uses 先約 (せんやく).

• あいにく先せん口くちがあって、その日ひは伺うかがえません。

  Unfortunately, I have a prior engagement and cannot visit that day.