the (wooded) promontory
An Ros has been the official Irish form of Rush since the passing of the first Placenames Order in 1975 (see http://www.irishstatutebook.ie/eli/1975/si/133/made/ga/print). The index cards from the time (see scanned images attached) make it clear that the researchers involved were well aware of the erstwhile identification of Rush with the historical place-name Ros Eo, found in early Irish sources. This identification was regarded by them as being almost certainly incorrect, and a review of the evidence available yields nothing to counter that opinion.

The absence of any reflex of Eo in all verifiable historical examples of the placename from the early thirteenth century onwards strongly indicates that (An) Ros was the form of the name used over hundreds of years prior to the ultimate decline of Irish in County Dublin.

The early evidence from the Irish language sources also contradict any earlier identification of Rush with Ros Eo. Early examples of the latter name are recorded in the Irish calendars of saints, such as the Martyrology of Tallaght, where ‘Cuannae uirginis i mMaig Locha i mBregaib .i. i rRus Eo’ “the virgin Cuanna in Maigh Locha in Breagha, i.e., in Ros Eo” is commemorated on the 10th April. Another martyrology which was compiled about the same time as that of Tallaght (*c.*800), namely The Martryology of Aengus, Cuanna is said to be ‘ó [from] Ros Eo’, and in one of the notes appended to this entry in a manuscript copy this is glossed as ‘ó Rus eo im-Maig Lacha i n-iarthar Breg’, which was translated by the editor of the text as “of Ros Eo in Mag Lacha in the west of Bregia”. As we know from the many extant references, the territory of Breagha (early dative form Bregaib, genitive Breg; standardized Mod. Ir. Breá; sometimes latinized Bregia, as above) included not alone north Co. Dublin but also some of the adjoining parts of Co. Louth and most of modern Co. Meath. Crucially, in the examples cited, Ros Eo was said to be located in Maigh Locha/Lacha “plain of the lake” in Breagha, and more specifically in the west of that territory. Two plausible locations for Magh Locha have been suggested by scholars — Moylagh (#1902) in the barony of Fore in the west of Co. Meath, or ‘Moylagh als. Castletown-Moylagh’ at Castletown in the parish of Rathmolyan, south of Trim and directly west of Summerhill (#39136).

The only controversy about the location of Ros Eo in Co. Meath arises from a single reference in the Martyrology of Gorman, compiled about 1170. As has been seen, the Martyrology of Tallaght locates Ros Eo at Maigh Locha in the west of Breagha — but the corresponding entry in the later Martyrology of Gorman renders this as ‘ó Ros Eó i Muigh Locha i n-Airthiur Breg’ “Ros Eo in Maigh Locha in the east of Breagha”. This one reference appears to have caused John O’Donovan, in an editorial note which he appended to his edition of the Annals of the Four Masters, to identify Ros Eo with Rush, Co. Dublin. O’Donovan’s identification was subsequently accepted by others, and found its way into early-20th century gazetteers of Irish placenames.

However, given that glosses on earlier texts locate Ros Eo in the west of Breagha (where there are indeed places called Maigh Locha), the later iteration in the Martyrology of Gorman is more likely to be the result of a copyist’s error. Salient in this regard is another reference in the Martyrology of Gorman to Colmán of Inch, a solidly identifiable location just north of Gorey and south of Arklow, in east Leinster. The explanatory gloss in the Martyrology of Aengus gives the correct information ‘Colmán .i. ó Inis mo Cholmóc in Huib Enechlais il Laignib, i n airthir Laigen’ “Colmán i.e. from Inis Mocholmóg…in the east of Leinster”. The later version in the Martyrology of Gorman, however, changes this gloss to ‘Colman…Innsi mo Cholmóc…in íarthar Laighen’ “Colmán of Inis Mocholmóg in west Leinster”. The later source has once again confused iarthar and oirthear in the original text.

In light of this textual evidence, and, moreover, given the fact that there are two locations in Meath identifiable with historical Maigh Locha, it is clear that the single reference to Ros Eo being in “east Leinster” must be erroneous — mirroring the same source's error regarding Colmán of Inch in Co. Wexford — thus explaining why not a single historical reference to Rush, Co. Dublin, contains a reflex of Irish Ros Eo. The researchers of the day, and the Placenames Commission who reviewed their evidence for the original Irish form of anglicised Rush, realized that nothing but (An) Ros would be satisfactory. This was the form put to public consultation in the 1960s and ultimately made official in 1975.
[PÓC; CÓC; AMGC]