Ó Siadhail / uaSiadhail / uaSiadgail is a Gaelic-Irish surname.
Overview.
There were at least three families of this name in Gaelic Ireland.
Little is recorded of the Ui Maine family. Those of Uí Failghe and Tír Chonaill were ollamhs of medicine, hereditary physicians to the ruling families in the respectives kingdoms and environs. It is not clear if the two were branches of the one family, or unrelated families who happened to bear the same surname.
One of the Ó Siadhail branches were physicians in service to the McMahons of Oriel, and later to the O'Neills. In the 1580s, this branch relocated from Brosna, County Kerry to Moycashel, County Westmeath.
Current forms.
The surname is now generally anglicised as O'Shiel, Shiel, Sheil, Sheils, Sheals, Sheal, and Sheilds (or Shiels, Shields as well as O’Shields), but the original form, Ó Siadhail, is used by persons who are Gaelic and conscious of their genealogy.
Notable bearers.
Notable people named Ó Siadhail or one of its variants include: