rule

Concise Oxford English Dictionary © 2008 Oxford University Press:
rule/ruːl/

▶noun

• 1 a regulation or principle governing conduct or procedure within a particular area of activity.

  ■ a code of practice and discipline for a religious community: the Rule of St Benedict.

• 2 control or government: an end to British rule.

• 3 (the rule) the normal or customary state of things.

• 4 a straight strip of rigid material used for measuring; a ruler.

• 5 a thin printed line or dash.

▶verb

• 1 exercise ultimate power over (a people or nation).

  ■ exert a powerful and restricting influence on.

  ■ informal be very good or the best.

• 2 pronounce authoritatively and legally to be the case.

• 3 (often as adj. ruled) make parallel lines on (paper).

• 4 (rule something out/in) exclude (or include) something as a possibility.

– phrases
as a rule usually, but not always.
rule of law the restriction of power by well-defined and established laws.
rule of the road a custom or law regulating the direction in which two vehicles should move to pass one another on meeting to avoid collision.
rule of thumb a broadly accurate guide or principle, based on practice rather than theory.
rule the roost be in complete control.

– derivatives
ruleless adjective.

– origin ME: from OFr. reule (n.), reuler (v.), from late L. regulare, from L. regula ‘straight stick’.