patronymic - name from the father (pater). E.g. the son of John (no surname) would become Johnson. A Eustace from Norman France might have a son called James, and he would then be James Eustace. Thus, in the early stages, lots of people got to be called Eustace (or Johnson) who were not at all related to each other. Cf McGregor, fitzAllan, O'Connor etc.)