What is Duplicatum Jus?

Legal Definition
A twofold or double right. Those words, according to Bracton, lib. 4, c. 3, signify the same as dreit dreit, or droit droit, and are applied to a writ of right, patent, and such other writs of right as are of the same nature, and do, as it were, flow from it, as the writ of right. Booth on Real Actions, 87.
-- Bouviers Law Dictionary
Legal Definition
Double right Bract, fol. 283b. See Droit-Droit.
-- Black's Law Dictionary
Legal Definition
A double right.
-- Ballentine's Law Dictionary