"Ar or Ard signifies a height, mountain, hill, elevation, the highest, noble, chief, &c. &c., and Ar in Hebrew, Chaldean, and Armenian, has the same meaning. Magh is a field, a plain, ground, &c., as well as a town, dwelling, &c."
Now, the topographical description of the county of Armarh is that it is hilly, and the hills (not very high) are of granite rock. The town of Armagh again is described as situated on an eminence. I suggest, therefore, the high field or ground, or the field of the Hill, or the dwelling or town of the Hill, as very natural derivations.
If your correspondent prefers it, Ar bears also the signification of rock, and M. Bullet says:—
"Ce terme nous a été conservé dans la Vie de Saint Colomb."
Who knows, therefore, whether in building the monastery alluded to by Camden, he may not have given it the name of
The dwelling of the Rock?
The Celtic language affords many other possibilities, but an accurate knowledge of the locality is requisite in judging of their probablility.
HERMES.
The etymology of Armagh, in Ireland, is very simple. Ard, high, great, noble, a purely Celtic root, found in many languages. Latin, Arduus, high, &c. Welsh, hardh, fair, handsome, &c. Magh, a plain, a level tract of land, a field. Ardmugh, the great plain. Others derive it from Eamhuin-magh, from the regal residence of the kings of Ulster, that stood in its vicinity; but the former is considered by those best capable of judging as the most correct. The original name was Druim-sailech, "the hill of sallows," which was changed to Ard-sailech, "the height of sallows," and then again to Ardmagh. Although now spelt Armagh, it was formerly more correctly written Ardmagh, which is undoubtedly the proper way.
HIBERNICUS