tanistry
Noun
Meaning
In Ireland, a tenure of family lands by which the proprietor had only a life estate, to which he was admitted by election.
Source: Webster's dictionaryExamples
As the average life span increased, an eldest son was more likely to reach majority age before the death of his father, and primogeniture became increasingly favoured over proximity, tanistry, seniority and election.
Popular assemblies, as in Ireland, were involved in law-making, and sometimes in king-making, although the introduction of tanistry —naming a successor in the lifetime of a king—made the second less than common.
For tanistry, etc., in Ireland, see Ó Cróinín, Early Medieval Ireland, 63–71.