The Nuttall Encyclopedia
A method of tenure which prevailed among the Gaelic Celts; according to this custom succession, whether in office or land, was determined by the family as a whole, who on the death of one holder elected another from its number; the practice was designed probably to prevent family estates falling into the hands of an incompetent or worthless heir.
Wood, James, ed. Entry for 'Tanistry'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/t/tanistry.html. Frederick Warne & Co Ltd. London. 1900.