鉄てっ則そく

noun

ironclad rule; inviolable rule; iron law

A firm, unbreakable rule or principle that must be followed without exception. Often used in formal or serious contexts.

• 安あん全ぜん確かく認にんは工こう事じ現げん場ばの鉄てっ則そくだ。

  Safety checks are an ironclad rule at construction sites.

• 彼かれは「約やく束そくを守まもるのが鉄てっ則そくだ」と言いった。

  He said, 'Keeping promises is an inviolable rule.'