established rule; law
A formal, fixed rule or law, often used in legal, scientific, or organizational contexts. Slightly stiff; in everyday speech 規則 or ルール is more common.
Please proceed according to this established rule.
The laws of physics are verified through experiments.
Compound of 定 (fixed, established) and 則 (rule, law). The exact historical derivation is uncertain, but the word follows a common Sino-Japanese pattern for formal terms.