| O'Dea | |
| Language: | English, from Irish |
| Meaning: | Descendant of Deághaidh (an Irish chieftain) |
| Derivation: | Irish: Ó Deághaidh |
| Region: | County Clare, Ireland |
O'Dea (; ga|'''Ó Deághaidh'''|italics=no, formerly Irish: Ua Deághaidh), is an Irish surname derived from Irish: Deághaidh, the name of a tenth-century clan chieftain.[1] According to historian C. Thomas Cairney, the O'Deas were one of the chiefly families of the Dal gCais or Dalcassians who were a tribe of the Erainn who were the second wave of Celts to settle in Ireland between about 500 and 100 BC.[2]
The O'Dea clan, also found as O'Day or just Day, came originally from County Clare in Ireland where there is a fortified tower house over 500 years old known as O'Dea Castle[3] at the 80acres townland of Dysert O'Dea .[4] The ruins of the Dysert O'Dea Monastery, round tower, and St. Tola's high cross are 265 metres to the south-southwest of the castle in the adjacent 260acres townland of Mollaneen,[5] near Corofin.[6] (52.9114°N -9.0664°W)
Edward MacLysaght, the former Chief Herald of Ireland, writing in his book, Irish Families, began his discussion of the O'Dea family as follows:
In another book, The Surnames of Ireland, MacLysaght describes the O'Deas as "one of the principal Dalcassian septs", and about the name itself, he remarks, "The prefix O is now almost always used, but a century ago Dea was quite usual and the surname Day was regarded as synonymous."[7]
The O'Deas – together with the O'Quinns (ga|Ó Cuinn|links=no) and the O'Griffins (ga|Ó Gríofa|links=no) – belonged to the Irish: Uí Fearmaic group, which was a branch of the Dalcassian tribe.[8]