Rule  —n. 1 compulsory principle governing action. 2 prevailing custom or standard; normal state of things. 3 government or dominion (under british rule). 4 graduated straight measure; ruler. 5 code of discipline of a religious order. 6 order made by a judge or court with reference to a particular case only. 7 printing thin line or dash. —v. (-ling) 1 dominate; keep under control. 2 (often foll. By over) have sovereign control of (rules over a vast kingdom). 3 (often foll. By that) pronounce authoritatively. 4 a make parallel lines across (paper). B make (a straight line) with a ruler etc.  as a rule usually. Rule out exclude; pronounce irrelevant or ineligible. Rule the roost be in control. [latin regula]