NON CONCESSIT, Eng. law. The name of a plea by which the defendant denies that the crown granted to the plaintiff by letters patent, the rights which he claims as a concession from the king; as, for example, when a plaintiff sues another for the infringement of his patent right, the defendant way deny that the crown has granted him such a right.

2. The plea of non concessit does not deny the grant of a patent, but of the patent as described in the plaintiff's declaration. 3 Burr. 1544; 6 Co. 15, b.