rule (nom)
Sens 1 : an official instruction that says how things must be done or what is
allowed, especially in a game, organization, or job. [source : LG]
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Sens 2 : what you should do in a particular situation, or a statement about this. [source : LG]
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Sens 3 : something that is normal or usually true. [source : LG]
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Sens 4 : a statement about what is usually allowed in a particular system, such
as the grammar of a language, or a science. [source : LG]