Definition of "rule"
A regulation, law, guideline.
A ruler; device for measuring, a straightedge, a measure.
A straight line (continuous mark, as made by a pen or the like), especially one lying across a paper as a guide for writing.
A regulating principle.
A normal condition or state of affairs.
To regulate, be in charge of, make decisions for, reign over.
To mark (paper or the like) with rules (lines).