Translation according to P. W. Joyce:
Killarah in Cavan ; church of the rath. See Rath.? Killarainy in Galway, and Killaranny in King's Co.; Coill-a'-raithnighe, wood of the ferns. See Raithneach, vol. ii. p. 330 [reproduced below].
Fern. As many of the common kinds of fern grow in this country in great abundance and luxuriance, they have, as might be expected, given names to numerous places. The simplest form of the Irish word for the fern is raith, which is used in some very old documents; but this form is wholly forgotten in the modern language, and I cannot find that it has been perpetuated in names. The nearest derivative is Rathain [rahen], which is the Irish name (as we find it in many old documents) of the parish of Rahan in King's County, well known in ecclesiastical history as the place where St. Carthach was settled before he founded his great establishment at Lismore. This name, which signifies a ferny spot, occurs in several other parts of Ireland. The Mac Sweenys had a castle at a place called Rahan near Dunkineely in Donegal, which the Four Masters call Rathain; there is a parish in Cork, near Mallow, with the same name, and several places in different counties have the names Rahin and Rahans - all meaning the same thing. The common word for the fern is raithne or raithneach [rahna], which latter form is found in Cormac's Glossary, and is used by the Irish-speaking peasantry all over the country at the present day. One of its diminutives, Raith-neachán, in the anglicised form Ranaghan (a fern-growing spot) is the name of places in each of the four provinces. All the preceding forms are further illustrated in the following names. Ardrahan, a small village in the county Galway, containing an old castle and a small portion of the ruins of a round tower, is often mentioned in the annals by the name of Ard-rathain, ferny height; and this also is the name of two townlands in Kerry, and of one near Galbally in Limerick. There are several places in different counties called Drumrahan, Drumraine, Drumrane, Drumrainy, and Drumrahnee, all signifying the ridge of the ferns.