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.
安全確認は工事現場の鉄則だ。
Safety checks are an ironclad rule at construction sites.
彼は「約束を守るのが鉄則だ」と言った。
He said, 'Keeping promises is an inviolable rule.'