unwritten law

noun

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, especially in cases involving relations between the sexes: sometimes urged in justification of persons guilty of criminal acts of vengeance.

unwritten law

noun

1. the law based upon custom, usage, and judicial decisions, as distinguished from the enactments of a legislature, orders or decrees in writing, etc

2. the tradition that a person may avenge any insult to family integrity, as used to justify criminal acts of vengeance

Word History and Origins

Origin of unwritten law¹

First recorded in 1635–45

Idioms and Phrases

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]