Mortmain. The lord’s right to a share of his men’s personal estate after death. (Duby, Georges. Rural Economy and Country Life in the Medieval West, 555)
*term retrieved from Netserf Medieval Glossary
From the Statute of Quia Emptores, 1290, on the buying and selling of land
And if he shall have sold to anyone any part of those his lands or tenements, the infeudated person shall hold that (part) directly of the lord in chief, and shall straightway be charged with as much service as pertains or ought to pertain to that lord for that parcel, according to the quantity of the land or tenement sold; and so in this case there shall fall away from the lord in chief that part of the service which is to be performed by the hand of the infeudator, from the time when the infeudated person ought to be attendant and answerable to that same lord in chief, according to the quantity of the land or tenement sold, for that parcel of service thus due. And it must be known that by the said sales or purchases of lands or tenements, or any part of them, those lands or tenements in part or in whole, may not come into mortmain, by art or by wile, contrary to the statute recently issued on this point.