Ó Marcacháin
Ó MARCACHÁIN—I—O Markaghaine, O Marcahan, Markahan, Markan, (Markham), Ryder; 'descendant of Marcachán' (diminutive of marcach, a rider); the name of an offshoot of Cinel Guaire, in south-west of Co. Galway. The family has been long settled in Thomond, where the name is now generally anglicised Markham. Ryder, which is in use in some places, is a translation.
Alphabetical Index to Irish Surnames