Definition of rule:

part of speech: verb

To govern; to conduct; to direct; to determine, as a court of justice; to decide; to lay down and settle; to exercise supreme authority.

part of speech: noun

An instrument by which straight lines are drawn, or short lengths measured; something established for guidance and direction; government; supreme command; control; a prescribed mode of operation by which certain results may be obtained; in gram., a statement by which some established order in the construction of words is expressed.