Aidhne ( ), also known as UàFhiachrach Aidhni, Mag nAidni, later Maigh Aidhne ("Plain (of) Aidhne"), was the territory of the UàFhiachrach Aidhni, a túath (tribal kingdom) located in the south of what is now County Galway in the south of Connacht, Ireland. (Aidhne is nominative case, Aidhni genitive). Aidhne is coextensive with the present diocese of Kilmacduagh.
The territory of Aidhne is bounded on the west by Loch Lurgan (Galway Bay) and the barony of Burren in County Clare in the province of Munster. County Clare also bounds Aidhne on its south and south-east side. Aidhne is bounded on the east by the low mountains of Sliabh Echtghe / Slieve Aughty (modern Sliabh EachtaÃÂ), which separate UàFhiachrach Aidhni from the territory of UàMaine (modern UàMhaine) in eastern County Galway. On the north-east Aidhne is bounded by the plains of UàMhaine and on the north by Mag Mucruime (modern Má Mucraimhe, the area around Athenry). On the north-west Aidhne is bounded by the parish of Mearaà(earlier Medraige, Meadhraighe) / Maree (Ballynacourty, Baile na Cúirte) which is in the territory of UàBriúin Seola (modern UàBhriain Seola).
In placename lore the kingdom took its name from the mythological Aidhne, one of the ten daughters of Partholón by his wife Delgnat. Aidhne was married to Breac.
The actual origin of the name may be from the Old Irish word ', meaning "aged, old"; perhaps the Aidhne were considered the oldest tribe in the area, in comparison to other peoples who had arrived more recently.
Historical tribes in Aidhne included the Hy-Fiachrach, the Ciarraighe Oga Beathra, the Tradraighe of Dubh-ros, and the Caonraighe of Art Aidhne.
In a later age, a branch of the Fir Bolg made Aidhne their home. Dubhaltach Mac Fhirbhisigh's Book of Genealogies states that the Tuath mhac nUmhóir[settled in]in Dál gCais and in UàFhiachrach of Aidhne. Their leader is given as Conall Caol, son of Aonghus mac ÃÂmhór. Conall was killed at the Battle of Maigh Mucruimhe in 195 CE, and his body brought back to Aidhne where it was interred at a leacht called Carn Chonaill (itself the site of a major battle some centuries later).
The territory of UÃÂ Fhiachrach Aidhni is coextensive with the diocese of Cill Mhic Dhuach / Kilmacduagh, which contains the civil parishes of Kinvarradoorus, Killinny, Killeenavarra, Drumacoo, Kilcolgan, Ardrahan, Stradbally, Killeeneen, Killeely, Killora, Killogilleen, Kilchreest, Isertkelly, Killinan, Kilthomas, Kilbeacanty, Beagh, Kilmacduagh, and Kiltartan. The diocese of Kilmacduagh contains the present Catholic parishes of Kinvara, Ballinderreen, Gort, Ardrahan, Craughwell, Beagh, Kilbeacanty, Kilthomas (Peterswell), Clarinbridge, and Kilchreest.