Mortmain n. (Law) Possession of lands or tenements in, or conveyance to, dead hands, or hands that cannot alienate. Note: The term was originally applied to conveyance of land made to ecclesiastical bodies; afterward to conveyance made to any corporate body.
... everywhere been putting into the hands of laymen the administration of civil justice. He had considerably increased the percentage to be paid on real property acquired by the Church (called possessions in mortmain), by way of compensation for the mutation-dues which their fixity caused the State to lose. At the time of the crusades the property of the clergy had been subjected to a special tax of a tenth of the revenues, and ... — A Popular History of France From The Earliest Times - Volume II. of VI. • Francois Pierre Guillaume Guizot