A Letter of Marque was a document given to a privateer or corsair that gave them amnesty from piracy laws if the plundered vessels were of an enemy nation. Of course the plunder was then eligible for tax but, nonetheless, the privateers still earned an awful lot more than any sailor serving in any Navy. It was a risky business but highly profitable. Today the term is usually associated with businessmen, politicians, bankers who manage to legitimise dodgy dealings via wily lawyers and spin.
