Wiktionary
n. (context historical English) A tribe or group of people in Ireland, having a loose voluntary system of governance entered into through contracts by all members.
Wikipedia
Túath (plural túatha) was a medieval Irish polity smaller than a kingdom. The word is from Old Irish and is often translated as "people" or "nation". It is cognate with the Welsh and Breton tud (people), Galician toudo, and with Germanic þeudō (for which see theodiscus).
"Túath" referred to both a geographical territory and the people who lived on that territory. In Modern Irish, it is spelled tuath, without the fada (length mark), and means "countryside".
In ancient Irish terms, a household was reckoned at about 30 people per dwelling. A trícha cét ("thirty hundreds"), was an area comprising 100 dwellings or, roughly, 3,000 people. A túath consisted of a number of allied trícha céta, and therefore referred to no fewer than 6,000 people. Probably a more accurate number for a túath would be no fewer than 9,000 people.
Usage examples of "tuath".
Armagh, king of Tuath Infochla four hundred years before, drove his ships of war from Falcarragh to Inish Thuaidh, where the mage-lights had first shone in the Eldest Time and where they glowed brightest.
Mallaghan might proclaim himself king over Tuath Gabair, but in truth, his rule only extended to the small towns, the villages, and the occasional squares of farmed land: tamed patches of a landscape that had seen vast, misty centuries when legends walked alive.
Order still attracted occasional acolytes from Inish Thuaidh, young men sent to serve by wealthy families, mostly, and even a few from among the mainland Riocha, primarily from Falcarragh in Tuath Infochla.
Gabair, whose birth name was Torin Mallaghan, in his court with the Riocha of Tuath Gabair gathered around him.
Most of them wore the green and brown of Tuath Gabair, though there were a few with the red and white of Tuath Airgialla, or the blue and black of Tuath Locha Lein.
Cianna drifted over to them before he could say more, with Tiarna Galen Aheron of Tuath Infochla accompanying her.
Tuath Connachta is gathering an army and that they may attack Tuath Gabair?
It was as if she were a bird, hovering far above Tuath Gabair and looking down.
Though the land at the northern borders of Tuath Gabair was sparsely populated and they were traveling overland rather than on the road, the area seemed oddly empty.
The bodies, Jenna noted, all wore the blue and gold of Tuath Connachta.
Tuath Connachta above Keelballi, near the northern border with Tuath Infochla.
Gabair, or perhaps the Tanaise Rig-they must have planned this not long after the mage-lights appeared in Tuath Gabair.
Ard has ended the conflict between Tuath Connachta and Tuath Gabair, and that he is actively working to have the Tuatha join together.
Longroot, mage-lights reappear over the village of Ballintubber in Tuath Gabair.
In traveling, he came to Tuath Gabair and the village of Ballintubber, where he fell in love with and married a woman named Maeve Oldspring.