A now-disused term referring to the aggregate of ancient international commercial and merchant customs.
As John Bouvier defined the term in his Law Dictionary:
"The general body of commerce usages in matters relative to commerce. It is a system of law which does not rest exclusively on the positive institution and local customs of any particular country, but consists of certain ... usages of trade which general convenience and a common sense of justice have established to regulate the dealings of merchants and mariners in all the commercial countries of the civilized world."
The legacy of law merchant (also known as mercantile law) in the common law and civil law is considerable. The law of negotiable instruments, of bills of lading, of international carriage and maritime law are in part or wholly derived from the ancient tenets of law merchant.
Latin: lex mercatoria.