Translation according to P. W. Joyce:
Doon or Don, a fort, an ancient royal residence :see vol. i. p. 277 [reproduced below].
Dun. The primary meaning of the word dun is "strong" or "firm," and it is so interpreted in Zeuss, page 30 :- "Dun, firmus, fortis." In this sense it forms a part of the old name of Dunluce castle, near the Giant's Causeway - Dunlios as it is called in all Irish authorities. Dunlios signifies strong lis or fort - the word is used by Keating, for instance, in this sense (see Four M., V. 1324f) - and this name shows that the rock on which the castle ruins stand was in olden times occupied by a fortified lis. It has the same signification in Dunchladh [Dunclaw], i.e. fortified mound or dyke, the name of the ancient boundary rampart between Brefny and Annaly, extending from Lough Gowna to Lough Kinclare in Longford; a considerable part of this ancient entrenchment is still to be seen near Granard, and it is now well known by the anglicised name of Duncla. As a verb, the word dun is used in the sense of "to close," which is obviously derived from its adjectival signification; and this usage is exemplified in Corragunt, the name of a place in Fermanagh, near Clones, which is a corruption from the Irish name, Corradhunta (change of dh to g, page 56), i.e. closed or shut up corra or weir. Dun, as a noun, sifnifies a citadel, a fortified royal residence; in the Zeuss MSS. It glosses arx and castrum; Adamnan translates it munitio; and it is rendered "pallace" by Mageoghegan in his translations of the Annals of Clonmacnoise: - "He builded seven downes or pallaces for himself." It is found in the Teutonic as well as in the Keltic languages - Welsh, din; Anglo-Saxon, tún; old high German, zun. It is represented in English by the word town; and it is the same as the termination dunum, so common in the old Latinised names of many of the cities of Great Britain and the Continent.This word was anciently, and is still, frequently applied to the great forts, with a high central mound, flat at top, and surrounded by several - very usually three - earthen circumvallations. These fortified duns, so many of which remain all over the country, were the residences of the kings and chiefs; and they are constantly mentioned as such in the Irish authorities. Thus we read in the Feast of Dun-na-ngedh (Battle of Maghrath, p. 7), that Domhnall, son of Aedh, king of Ireland from A.D. 624 to 639, "first selected Dun-na-ngedh, on the banks of the Boyne, to be his habitation, … and he formed seven very great ramparts around this dun, after the model of the houses of Tara." And other passages to the same effect are cited at page 268 et seq. In modern names, dun generally assumes the forms dun, doon, or don; and these syllables form the beginnings of the names of more than 600 townlands, towns and parishes. There are twenty-seven different places called Doon; one of them is the village and parish of Doon in Limerick, where was situated the church of St. Fintan; the fort from which the place received the name, still remains, and was anciently called Dunblesque, Dunamon, now a parish in Galway, was so-called from a castle of the same name on the Suck; but the name, which the annalists write Dun-Iomgain, Imgan's fort, was anciently applied to a dun, which is still in part, preserved. Dundonnell, i.e. Donall's or Domhnall's fortress, is the name of a townland in Roscommon, and of another in Westmeath; and Doondonnell is a parish in Limerick; in Down it is modified, under Scottish influence, to Dundonald, which is the name of a parish, so called from a fort that stands not far from the church. The name of Dundalk was originally applied, not to the town, but to the great fortress now called the moat of Castletown, a mile inland; there can be no doubt that this is the Dun-Dealgan of the ancient histories and romances, the residence of Cuchullin, chief of the Red Branch Knights in the first century. In some of the tales of the Leabhar na hUidhre, it is called Dun-Delca, but in later authorities, Dun-Dealgan, i.e. Delga's fort; and according to O'Curry, it received its name from Delga, a Firbolg chief who built it. The same personal name appears in Kildalkey in Meath, which in one of the Irish charters in the Book of Kells, is written Cill-Delga, Delga's church. There is a townland near Lisburn, now called Duneight, but written Downeagh in an Inquisition of James I., which has been identified by Dr. Reeves with the place called in the "Circuit of Ireland" Dun-Eachdhach, Eochy's fortress: where the great king Muircheartach of the leather cloaks, slept a night with his men, when performing his circuit of the country in the year 941. There is a parish in Antrim, and also a townland, called Dunaghy, which is the same name more correctly anglicised. The celebrated rock of Dunamase in Queen's County is now covered by the ruins of the O'Mores' castle, but it must have been previously occupied by a dun or caher. In an Inquisition of Richard II., it is called Donemaske, which is a near approach to its Irish name as we find it in the Annals, viz., Dun-Masg, the fortress of Masg, who was grandson of Sedna Sithbhaic (Sedna-Sheevick), one of the ancestors of the Leinster people A great number of these duns, as will be seen from the peceding , have taken their names from persons, either the original founders or subsequent possessors. But various other circumstances, in connection with these structures, were seized upon to form names. Doneraile in Cork, is called in the Book of Lismore, Dun-air-aill, the fortress on the cliff, but whether the dun is still there I cannot tell. There is a parish in Waterford whose name has nearly the same signification, viz., Dunhill; it is called in Grace's Annals Donnoil, which very well represents the Irish Dun-aill, the fortress of the cliff. It is understood to have taken its name from a rock on which a castle now stands; but a dun evidently preceded the castle, and was really the origin of the name. Doonally in the parish of Calry, Sligo (an ancient residence of the O'Donnells), which the Four Masters write Dun-aille, and which is also the name of several townlands in Sligo and Galway, is the same name, but more correctly rendered. Of similar origin to these is Dundrum in Down, which the Four Masters mention by the name of Dundroma, the fort on the ridge or long hill; the original fort has however disappeared, and its site is occupied by the well-known castle ruins. There are several other places called Dundrum, all of which take their name from a fort on a ridge; the ancient fort of Dundrum, near Dublin, was most probably situated on the height where the church of Taney now stands. Although the word dun is not much liable to be disguised by modern corruption, yet in some cases it assumes forms different from those I have mentioned. The town of Downpatrick takes its name from the large entrenched dun which lies near the Cathedral. In the first century this fortress was the residence of a warrior of the Red Branch Knights, called Celtchair, or Keltar of the battles; and from him it is variously called in Irish authorities Dunkeltar, Rathkeltar, and Araskeltar (aras, a habitation). By ecclesiastical writers it is commonly called Dun-leth-glas, or Dun-da-leth-glas; this last name is translated, the dun of the two broken locks or fetters (glas, a fetter), which Jocelin accounts for by a legend - that the two sons of Dichu (see p. 113), having been confined as hostages by king Leaghaire, were removed from the place of their confinement, and the two fetters by which they were bound were broken by miraculous agency. "Afterwards, for brevity's sake, the latter part of this long name was dropped, and the simple word Dun retained, which has past into the Latin Dunum, and into the English Down" (Reeves Eccl. Ant., p. 143). The name of St. Patrick was added, as a kind of distinctive term, and as commemorative of his connection with the place. Down is the name of several places in King's County and Westmeath; and the plural Downs (i.e. forts) is still more common. The name of the Glen