The surname Adair derives from the Olde English pre 7th Century personal name Eadgar, a compound of the elements ead meaning Prosperity-spear. It is of Irish and Scottish origin. The name is found in Medieval English in various forms i.e. Edgar, Adger, Agar etc., and is first recorded as Edgar in the Domesday Book of 1086, for Huntingdonshire. The surname from this source first appears in the mid 13th Century.
The Celtic and Gaelic origin of Adair is from Ath, a ford, and dare, from darach, the place of oaks, "The ford of the oaks." There is the following tradition of the origin of this surname: "Thomas, the sixth Earl of Desmond, while on a hunting excursion was benighted, and lost his way, between Tralee and Newcastle, in the county of Limerick, where he was received and hospitably entertained by one William McCormic, whose daughter he subsequently married. At this alliance, the family and clan took umbrage. Resigning his title and estate to his youngest brother, he fled to France in 1418, and died of grief at Rouen, two years afterward. The King of England attended his funeral. He had issue, Maurice and John; Robert, the son of Maurice, returning to Ireland, with the hope of regaining the estates and title of Thomas, his ancestor, slew Gerald, the White Knight, in single combat at Athdare, the ford of the oaks, whence he received the name of Adaire. He embarked for Scotland, where he married Arabella, daughter of John Campbell, Lord of Argyle."
Variations: Edgar, Eager, Eagger, Egar, Egarr, Ager, Adger Ireland- O'Daire