Kill a cyclist GBP500

no its not the definition of law.

Ok, the nitpicking about the exact definition of law notwithstanding... do you disagree that there's an implicit assumption of obedience in the term "law"?

And if one really wants to nitpick the definition of "law"...

According to your link:
S: (n) law, jurisprudence (the collection of rules imposed by authority)
S: (n) law (legal document setting forth rules governing a particular kind of activity)

According to the same site:
S: (n) rule, prescript (prescribed guide for conduct or action)

Unfortunately, if you look for the definition of "prescribed", you find a circular definition that isn't very helpful:
S: (adj) prescribed (set down as a rule or guide)

Here's a clearer definition:
http://dictionary.law.com/default2.asp?selected=1111&bold=||||
n. 1) any system of regulations to govern the conduct of the people of a community, society or nation, in response to the need for regularity, consistency and justice based upon collective human experience.

2) n. a statute, ordinance or regulation enacted by the legislative branch of a government and signed into law, or in some nations created by decree without any democratic process.

We see words like "rule" and "regulation", but nowhere is the requirement for obedience explicitly stated. So does that mean the requirement doesn't exist? Or simply that neither of us have found a definition that's good enough?

I'm no jurisprudence expert, but I'm sure there's a long complicated debate on the philosophy of legal authority buried in here...