This is another extract from P.W. Joyce's Irish Names of Places, Volume III, and tells of the meaning of the name Granard, in County Longford.
Granard, in the county Longford, is mentioned in the Tain-bo-Chuailgne in Leabhar-na-hUidhre (p. 57, col. a, line 30), a book written A.D. 1100. In the text it is written Gránairud, which is the oldest form of the name accessible to us, and a gloss immediately over the word—".i. Gránárd indiu" ("namely Granard to-day")—identifies Gránairud with the present Granard. Moreover, the gloss was written at the same time as the text, so that the name had taken the form Granard 800 years ago, Gránairud being a still older form. If we were profane enough to take liberties with this grand old text, we could easily, by a very slight twist, change Gránairud to an intelligible word; but there it stands, and no one can tell what it means.
But a name may be plain enough as to its meaning —may carry its interpretation on its face—and still we may not be able to tell what gave rise to it— why the place was so called. There are innumerable names all over the country subject to this doubt; but in these cases a little more liberty of conjecture is allowable. Moreover, local inquiry among the most intelligent of the old inhabitants often clears up the doubt. Still there are hundreds of names that remain, and will always remain, obscure in this respect.
You can find more information on the meaning of the name Granard, and hundreds (even thousands) of Irish place names on the wonderful website www.logainm.ie