rule / roōl/ • n. 1. one of a set of explicit or understood regulations or principles governing conduct within a particular activity or sphere: the rules of the game were understood. ∎  a law or principle that operates within a particular sphere of knowledge, describing or prescribing what is possible or allowable: the rules of grammar. ∎  a code of practice and discipline for a religious order or community: the Rule of St. Benedict. ∎  control of or dominion over an area or people: the revolution brought an end to British rule. ∎  (the rule) the normal or customary state of things: such accidents are the exception rather than the rule.2. a strip of wood or other rigid material used for measuring length or marking straight lines; a ruler. ∎  a thin printed line or dash, generally used to separate headings, columns, or sections of text.3. (Rules) Austral. short for Australian Rules (football). ∎  Law an order made by a judge or court with reference to a particular case only.• v. 1. [tr.] exercise ultimate power or authority over (an area and its people): Latin America today is ruled by elected politicians | [intr.] the period in which Spain ruled over Portugal. ∎  (of a feeling) have a powerful and restricting influence on (a person's life): her whole life seemed to be ruled by fear. ∎  [intr.] be a dominant or powerful factor or force: the black market rules supreme. ∎  pronounce authoritatively and legally to be the case: a federal court ruled that he was unfairly dismissed from his job. ∎  Astrol. (of a planet) have a particular influence over (a sign of the zodiac, house, aspect of life, etc.).2. [tr.] make parallel lines across (paper): [as adj.] (ruled) a sheet of ruled paper. ∎  make (a straight line) on paper with a ruler. PHRASES: as a rule usually, but not always.make it a rule to do something have as a habit or general principle to do something: I make it a rule never to mix business with pleasure.rule of law the restriction of the arbitrary exercise of power by subordinating it to well-defined and established laws.rule of thumb a broadly accurate guide or principle, based on experience or practice rather than theory.rule the roost be in complete control.PHRASAL VERBS: rule something out (or in) exclude (or include) something as a possibility: the doctor ruled out appendicitis.DERIVATIVES: rule·less adj.