noun
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.
この定則に従って手続きを進めてください。
Please proceed according to this established rule.
物理学の定則は実験によって確かめられる。
The laws of physics are verified through experiments.