Gleann is essentially a glen or valley, interestingly, according to P.W. Joyce the English word 'Glen', also used for valley, does not derive from the Irish Gleann, or vice versa, that it was previously in Anglo Saxon and was in Old Irish far before the coming of the Normans. My guess it could be they are both from Welsh, since in Welsh it's Glyn or perhaps they all share an indo-European root or another possibility it come from the influence of Irish missionaries christianising the Saxons, in other words, who knows! According to Joyce there are over 600 places in Ireland with the name Glan or Glen (which he points out are the anglicisations of Gleann) and the name is found in every county throughout the land.
The Gleann shown here is 'Glenmacnass' or in Irish ' Gleann Log an Easa' which according to Room translates as 'Glen of the hollow of the waterfall'. This Gleann is often mentioned in Geographic books as its kind of the epitomy of a U-Shaped Valley. You can see clearly when you are there, the U shape of the Glacier that cut its way slowly through this gleann, previous to that it would have been what they call a V shaped Valley, which are created by rivers. This one was probably created by the river shown here on the right, which derives its name from the Gleann, as its known as 'Glenmacnass River'.
Placenames are part of our identity, part of a living landscape, as Patrick Sheeran has said, if we were to visit Ayers Rock in Australia, it would seem like a nice geographic feature but not much more. But to the Aboriginals each area, each gap or rock has a name, knowing them conjures up stories and myths in their minds. The same would have been true here in ancient times, as Tim Robinson points out for the Celts, each gleann, forest, or mountain was inhabited by wonder and myth. Similar would have been true for the later Gael as Daniel Corkery puts it: " Those O'Connells, O'Connors, O'Callaghans, O'Donoghues, all the Gaels were one, it may be maintained, with the very landscape itself... to run off the family names connected with one of those houses was to call to vision certain districts hills, rivers and plains; while contrariwise, to recollect the place-names in certain regions was to remember the ancient tribes and their memorable deeds." So one can see how placenames are tied to a peoples sense of place and even further, they are part of their identity and the living landscape which they inhabit.
1. Irish Place Names- Deirdre Flanagan & Laurence Flanagan- Gill&MacMillan- 2002
2. An Irish-English dictionary, J. O'Brien, 1832,
3. Irish names of places, Vol 1, P.W. Joyce
4. Irish local names explained Vol1, P.W. Joyce, 1902
5. Folclóir Gaedhilge agus Béarla, Rev. Patrick S. Dinneen, 1904,
6. 'Dictionary of Irish Place Names', A. Room, 2009
7. OSI Discovery Map 56. 2001
8. The Kingfisher Geography Encyclopedia, 2001
9. The Dorling Kindersley Illustrated Factopedia, 1995
10. Genius Fabulae: The Irish Sense of Place, Patrick Sheeran, 1988
11. Listening to the Landscape, Tim Robinson, The Irish Review, No. 14, An Ghaeilge: The Literature and Politics of Irish(Autumn, 1993), pp. 21-32
12. Landscape and western Art