law merchant vs mercantile law

law merchant and mercantile law both are nouns.

Word	Noun	Adjective	Verb	Adverb
law merchant	Yes	No	No	No
mercantile law	Yes	No	No	No

As nouns, law merchant and mercantile law are synonyms defined as:

law merchant and mercantile law: the body of rules applied to commercial transactions; derived from the practices of traders rather than from jurisprudence

Other synonyms of law merchant include commercial law.

law merchant (noun)	mercantile law (noun)
the body of rules applied to commercial transactions; derived from the practices of traders rather than from jurisprudence	the body of rules applied to commercial transactions; derived from the practices of traders rather than from jurisprudence