1.a principle or condition that customarily governs behavior;

it was his rule to take a walk before breakfast

2.something regarded as a normative example;

the convention of not naming the main character

3.prescribed guide for conduct or action

4.(linguistics) a rule describing (or prescribing) a linguistic practice

5.a basic generalization that is accepted as true and that can be used as a basis for reasoning or conduct;

their principles of composition characterized all their works

6.a rule or law concerning a natural phenomenon or the function of a complex system;

the principle of the conservation of mass

7.the duration of a monarch's or government's power;

during the rule of Elizabeth

8.dominance or power through legal authority;

France held undisputed dominion over vast areas of Africa

9.directions that define the way a game or sport is to be conducted;

he knew the rules of chess

10. any one of a systematic body of regulations defining the way of life of members of a religious order;

the rule of St. Dominic

11. (mathematics) a standard procedure for solving a class of mathematical problems;

he determined the upper bound with Descartes' rule of signs

12. measuring stick consisting of a strip of wood or metal or plastic with a straight edge that is used for drawing straight lines and measuring lengths