rul·ing (rōṓlĭng)

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adjective 

1. Exercising control or authority: the ruling junta; ruling circles of the government.
2. Predominant: the ruling principle.

noun 

1. The act of governing or controlling.
2. An authoritative or official decision: a court ruling.

rule (rōōl)

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[Middle English reule, from Old French, from Vulgar Latin* regula, from Latin rēgula, rod, principle.]

noun 

1. 1. Governing power or its possession or use; authority.
   2. The duration of such power.
2. 1. An authoritative, prescribed direction for conduct, especially one of the regulations governing procedure in a legislative body or a regulation observed by the players in a game, sport, or contest.
   2. The body of regulations prescribed by the founder of a religious order for governing the conduct of its members.
3. A usual, customary, or generalized course of action or behavior: “The rule of life in the defense bar ordinarily is to go along and get along” (Scott Turow)
4. A generalized statement that describes what is true in most or all cases: In this office, hard work is the rule, not the exception.
5. Mathematics A standard method or procedure for solving a class of problems.
6. Law
   1. A court order limited in application to a specific case.
   2. A subordinate regulation governing a particular matter.
7. See ruler
8. Printing A thin metal strip of various widths and designs, used to print borders or lines, as between columns.

verb: ruled, rul·ing, rules. 

transitive verb 

1. To exercise control, dominion, or direction over; govern.
2. To dominate by powerful influence.
3. To decide or declare authoritatively or judicially; decree. See synonyms at decide
4. 1. To mark with straight parallel lines.
   2. To mark (a straight line), as with a ruler.

intransitive verb 

1. To be in total control or command; exercise supreme authority.
2. To formulate and issue a decree or decision.
3. To prevail at a particular level or rate: Prices ruled low.
4. Slang To be excellent or superior: That new video game rules!

phrasal verbs

rule out

To prevent; preclude: The snowstorm ruled out their weekly meeting.

To remove from consideration; exclude: The option of starting over has been ruled out.

idioms

as a rule

In general; for the most part: As a rule, we take the bus.

derivatives

ruĺa·ble

adjective