What does "tanistry" mean?

Tanistry: In Ireland, a tenure of family lands by which the proprietor had only a life estate, to which he was admitted by election. 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.