Ó Caisín
Ó CAISÍN—I—O Cashine, O Cassin, O Kessan, Casheen, Cashin, Cashen, Cashion, Cashon, Cassian, Cassin, Keshin; 'descendant of Caisín' (diminutive of cas, bent, curly); apparently a variant in the south of Ireland of the Ossory surname Mac Caisín, which see.
Alphabetical Index to Irish Surnames