mortmain

noun2

1. •
   The perpetual, inalienable possession of lands by a corporation or non-personal entity such as a church.

   • [W]e do hereby grant our especial license and authority unto all and every person […] to grant sell alien and convey in mortmain unto and to the use of the said Society and their successors […] — 1824
2. •
   (literary) A strong and inalienable possession.