law = behaviour regulation
nb. regulation = perception + effective response
An unambiguous definition. It does not presume a specific qualification or type of law. i.e. civil/criminal law. Often, law is defined with a 'silent qualification' (i.e. the silent k in knife) and it's generally civil/criminal. The above definition consists of the basic components law.
Behaviour regulation may serve as a stand in for 'law' in any sentence.
Law can be identified anywhere from subatomic particles to parliament. Studies into types behaviour regulation: i.e. Criminal, Civil, Chemical, Physical, Biological, Natural (natural selection) etc..
Wikipedia articles on law (for instance) refer only to civil and criminal forms of law.
Dictionary definitions are plenty but none as simple as the above.