The Collaborative International Dictionary of English v.0.48:

Tanistry \Tan"ist*ry\, n. [See Tanist.]
   In Ireland, a tenure of family lands by which the proprietor
   had only a life estate, to which he was admitted by election.
   [1913 Webster]

   Note: The primitive intention seems to have been that the
         inheritance should descend to the oldest or most worthy
         of the blood and name of the deceased. This was, in
         reality, giving it to the strongest; and the practice
         often occasioned bloody feuds in families, for which
         reason it was abolished under James I.
         [1913 Webster]