Translation according to P. W. Joyce:
Oughtagh in Galway, Derry, and Mayo; Uchtach or Ochtach, the breast (of a hill): from Ucht, the breast; with ach appended: p. 12 [reproduced below]. See vol. ii. p. 428 [reproduced below].
Ach, lach, nach, rach, tach, trach, seach. All these postfixes have a collective signification when placed after nouns and generally convey the sense of "full of", "abounding in", much the same as the English postfixes ful, y, and ous. In Irish writings, especially if they be ancient, these terminations are often written ech, lech, etc.; and sometimes, in compliance with a grammatical custom, they are changed to each, leach, etc.; but these changes do not influence the anglicised forms. Ach. This is the most common of all Irish terminations, and its most usual form in anglicised names is agh, which is sounded with a strong guttural by the people, but pronounced ah by those who cannot sound the guttural. Scart means a brake or scrubby place; and Scartagh, the name of a place near Clonakilty in Cork, signifies a place covered with brakes - a bushy spot. From draighen [dreen] the blackthorn or sloebush, we have draighneach, a place abounding in blackthorns; and this again compounded with cill, church, gives Cill-draighnech (so written in the Irish Calendars), the church of the sloe-bushes. It was one of the churches of St. Erinin or Mernoc (died, A. D. 635) who is mentioned by Adamnan in his Life of St. Columba, and who gave name to Inchmarnock and to the two Kilmarnocks in Scotland. This church has left its name on a townland, now called Kildreeenagh, in the parish of Dunleckny in Carlow, near Bagenalstown.
Breast. The front of a hill, a projection from its general body, is often designated by the word ucht, which signifies the breast. The most correct anglicised form is ught, which is seen in Ughtyneill near Moynalty in the county Meath, O'Neill's hill-breast (y for O: see p. 137, supra). But it more often takes the form ought; of which an excellent example is seen in Oughtmama, the name of a parish in Clare, meaning the breast or front of the maam or mountain pass - Oughtymoyle and Oughtymore in the parish of Magilligan in Derry, signifying bare breast and great breast respectively, the y being a corruption in both names. There is a small island in the eastern side of Lough Mask, about four miles south-west pf Ballinrobe, called Inishoght, the island of the breast; and the Four Masters mention another little island of the same name, which they call Inis-ochta, in Lough Macnean in Fermanagh, as the scene of a fight between the O'Rourkes and the MacRannalls in A.D. 1499. But this name, though used in the last century, is now forgotten; the present name of the islet is Inishee, i.e. Inis-Aedha, the island of Aedh or Hugh; and according to the tradition quoted by O'Donovan (Four M., IV. - p. 1250 m.) it received this name from a king named Aedh who once lived on it. Inishee or Hugh's Island is also the name of a place in the parish of Clonfert in the east of the county of Galway, including within it the village of Eyrecourt, now called Donanaghta; but in the Inquisitions the name is written Doonanought, bot of which point to the meaning, the fort of the breast, i.e. built on the breast of a hill.