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 aidhne, adna, adnae, meaning "aged, old"; perhaps the Aidhne were considered the oldest tribe in the area, in comparison to other peoples who had arrived more recently.[2][3][4]
Historical tribes in Aidhne included the Hy-Fiachrach, the Ciarraighe Oga Beathra, the Tradraighe of Dubh-ros, and the Caonraighe of Art Aidhne.[5]
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 Uí Fhiachrach of Aidhne. Their leader is given as Conall Caol, son of Aonghus mac Úmhór. Conall was killed at the Battle of Maigh Mucruimhe in 195 AD, 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 Uí 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, Kiltartan. The diocese of Kilmacduagh contains the present Catholic parishes of Kinvara, Ballinderreen, Gort, Ardrahan, Craughwell, Beagh, Kilbeacanty, Kilthomas (Peterswell), Clarinbridge, Kilchreest.