commandment
n. countable C1 Advanced US //kəˈmændmənt// UK //kəmˈɑːndmənt// com·mand·ment
n. an important rule that you must follow, often coming from a god or a powerful leader. People sometimes use this word for their own strict personal rules.
n. a divine or authoritative rule of conduct, specifically one of the ten biblical laws. Often used metaphorically to describe a fundamental principle that must be obeyed.
The first commandment is the most important one.
In this household, the first commandment is that everyone must take their shoes off at the door.
Inherited from Middle English comaundement, from Old French comandement, from comander. See command.
Usage
Often used in the plural when referring to a set of established rules.