规则

There is no cast-iron rule.

football rules

sanitary rules

spelling rules

fundamental/ground rule

playing rule

observe/obey traffic regulations; follow traffic regulations

make/formulate a regulation/rule; set down a rule/regulation

remodel/modify a regulation/rule

disregard a rule

break/infringe/violate a regulation/rule

natural law; law of nature

The coastline is very irregular.

unformed/free-form piece of wood

regular verb