From early times the Mac an tSionnaigh were widely scattered allowing their name to be anglicised phonetically in an extraordinary number of ways depending on local accents and dialects - MacAshinna, MacShanaghy, Shinny, Shannon, Shinnock, Tinney, MacAtinna are only some of the variations which have been noted.
O Sionnaigh has a more particular history. Tadhg O Catharnaigh ("Kearney") was Chief of Teffia in Co. Meath in the eleventh century and, for his wily ways, become known as "An Sionnach", the fox. As his descendants prospered even further, becoming proprietors of the entire barony of Kilcoursey in Co. Offaly and acquiring the title "Barons Kilcoursey", they adopted his nickname as their own surname in place of O Catharnaigh, and the chief of the family took on "The Fox" as a title. They lost their property after the rebellion of 1641/2, but the descent from the last duly inaugurated Chief has remained unbroken. John William Fox, The Fox, Chief of his Name, formerly recognised as such by the Chief Herald of Ireland, lives in Australia.