A Rule

1. A regulation, law, guideline.
2. A regulating principle.
3. The act of ruling; administration of law; government; empire; authority; control.
4. A normal condition or state of affairs.
5. (obsolete) Conduct; behaviour.
6. (law) An order regulating the practice of the courts, or an order made between parties to an action or a suit.
7. (mathematics) A determinate method prescribed for performing any operation and producing a certain result.
8. A ruler; device for measuring, a straightedge, a measure.
9. A straight line (continuous mark, as made by a pen or the like), especially one lying across a paper as a guide for writing.
10. (printing, dated) A thin plate of brass or other metal, of the same height as the type, and used for printing lines, as between columns on the same page, or in tabular work.