... The next son mentioned in the Will (of Cahirmore) is Dairĕ Barrach, who was the ancestor of a tribe called from him Hy Bairche (O'Dugan), the race of (Daire) Barrach...
    ... In the ancient Fenian tale called Cath Finntragha, or "The battle of Ventry," we are told that Dairĕ Dornmhar, "The monarch of the world," landed at Ventry to subjugate Erin, the only country yet unconquered;...
    Doire or daire [derry] is an oak wood, and is almost always represented in anglicised names by derry or derri.  The most ancient name of Londonderry, according to all our authorities, was Daire-Calgaich [Derry-Calgagh]; Adamnan, in one place, uses this name and elsewhere he translates it Roboretum-Calgachi, the oak wood of Calgach.  Calgach was a man's name common among the ancient Irish, signifying "fierce warrior;" and in the Latinized form of Galgacus, readers of Tacitus will recognise it, as the name of the hero who led the Caledonians at the battle of the Grampians.
    Daire Calgaich was the old pagan name used for ages before St. Columba erected his monastery there in 546; it was retained till the tenth or eleventh century, when the name Derry-Columkille began to prevail, in memory of its great patron, and continued down till the time of James I., whose charter, granted to a company of London merchants, imposed the name "Londonderry." (The Origin and History of Irish Names of Places, Joyce, v.1, 1869).