[a. Welsh Brython, Briton, Britons:—OCeltic Britton-, BRITON. Brython and Brythonic have been introduced by Prof. Rhŷs, to avoid the misleading associations which attach to the use of ‘Briton,’ ‘British,’ and ‘Cymric.’ They are the natural correlatives of Goidel and Goidelic, applied to the Scoto-Irish or Gaelic division of the Celtic stock.] A member of that great division of the Celts of the British isles, which mainly occupied South Britain; a Briton of Wales, Cornwall, or ancient Cumbria.
Hence Brythonic a. Of or pertaining to the Brythons, or Britons of Wales, Cornwall, and Cumbria, and their kin.
1884. Rhys, Celtic Britain, 3. The other group is represented … by the people of Wales and the Bretons…. The national name of those speaking these dialects was that of Briton;… we take the Welsh form of it, which is Brython, and call this group Brythons and Brythonic. Ibid., 4. Every Celt of the United Kingdom is, so far as language is concerned, either a Goidel or a Brython. Ibid., 208. Both the Brythonic and the Goidelic forms prove beyond doubt [etc.].
