"The judgment of a competent, court, until reversed or otherwise superseded, is law, as much as any statute." (Black's Law Dictionary, 1910)
American Heritage Dictionary
a. A statute, ordinance, or other rule enacted by a legislature.
b. A judicially established legal requirement; a precedent.
11. Unwritten or common law, a rule of action which derives its authority from long usage, or established custom, which has been immemorially received and recognized by judicial tribunals. As this law can be traced to no positive statutes, its rules or principles are to be found only in the records of courts, and in the reports of judicial decisions.
One will find similar entries in other dictionaries as well. Some will simply have general statements about binding rules, but where you find mention of statutes, look and see whether judicial precedent or "common law" is mentioned. I don't think you'll be disappointed. I've been told that this is an un-American approach, but I can live with that. Words have meaning after all, and as general rule, the dictionaries are great sources for those meanings.