Costello (surname) to a Gaelic translation of Jocelyn, Jocelyn d'Angulo's given name. In fact, MacOisdealbhaigh is the Gaelic translation of his brother Hostilo (or Hostilio) d'Angulo's first name. Oisdealbh is a much more obvious translation of Hostilo. It is Hostilo's descendants who would bear the surname Mac Oisdealbhaigh (son of Oisdealbh or Hostilo). The surname would later be anglicized to Costello, Costelloe, and Costellow. Gilbert d'Angulo is also sometimes listed as the son of Jocelyn d'Angulo in error. Gilbert d'Angulo is the father of both Jocelyn and Hostilo. It occasionally has been adopted as a pseudonym or stage name by famous people
Poland (surname) the examples where the 'Mac' or 'Mc' has been dropped can be explained for several reasons. In English controlled areas of Ireland (especially around The Pale), it was declared that the Irish take on names in an English form and many were required to do so in order to do business with the powers that be, or to obtain a tenancy on English controlled land. Census takers were also allowed to use either form, with or without the Gaelic prefix. It also was not uncommon for the 'Mac' or 'Mc' prefix to simply be incorporated into the surname to result