Source : Webster's Revised Unabridged Dictionary (1913)

Mortmain \Mort"main`\, n. [F. mort, morte, dead + main hand; F.
   main-morte. See {Mortal}, and {Manual}.] (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. --Burrill.

Source : WordNet®

mortmain
     n 1: real property held inalienably (as by an ecclesiastical
          corporation) [syn: {dead hand}]
     2: the oppressive influence of past events of decisions [syn: {dead
        hand}, {dead hand of the past}]