| 1. | a law that rests for its authority on custom, judicial decision, etc., as distinguished from law originating in written command, statute, or decree. |
| 2. | the unwritten law, the supposed principle of the right of the individual to avenge wrongs against personal or family honor, esp. in cases involving relations between the sexes: sometimes urged in justification of persons guilty of criminal acts of vengeance. |
unwritten law
An accepted although informal rule of behavior, as in It's an unwritten law that you lock the gate when you leave the swimming pool. [Mid-1400s]