Common law refers to the legal tradition that came down from England to the United States and the other English colonies.
Yes. In the U.K, there is no legislation that forbids Murder, only the Common Law of Judicial precedent.
"Common law" refers to decisions by courts of appeal and the highest court in a state or the US, which may be binding on the lower courts or used by them to guide their decisions in similar cases.
the king makes the laws like in a absolute monarchy
(in the US) There is no common law, all laws are now codified as statute laws - even those which formerly might have been "common law."