The toponym Cornouaille was established in the early Middle Ages in the southwest of the Breton peninsula. Prior to this, following the withdrawal of Rome from Britain, other British migrants from what is now modern Devon had established the region of Domnonea (in Breton) or Domnonée (in French) in the north of the peninsula, taken from the Latin Dumnonia.
The region was first mentioned in surviving records by a Cornouaille-related name between 852 and 857, when the
Anaweten, bishop of Saint-Corentin at Quimper Cathedral, took over Cornugallensis under the order of Nominoe, Duke of Brittany and Tad ar Vro. The names Cornwall and Cornouaille, like the surname Cornwallis, are from Corn-wealas. The first element is from the name of a Brythonic tribe Latinized as Cornovii, meaning 'peninsula people', from the Celtic kernou, 'horn, headland'. It is a cognate of the English word horn, both being from PIE *ker- 'uppermost part of the body, head, horn, top, summit',. The second element is the Anglo-Saxon suffix -wealas, from walh, a word used by the Germanic speakers for 'a non-Germanic foreigner', especially Celtic speakers but also sometimes used for Romance-language speakers. Walh is an element found in the words and names walnut, Walloon, Wales, Wallachia, Wallace, Walcheren, and Walsh.
A Corn-/Kern- name was used in reference to the resettling of the new wave Celts from Great Britain in formerly Dumnonian-seized lands. This is related to the difference between Grande-Bretagne (Great Britain) and Bretagne (Brittany) in French, with Brittany having originally been thought of a British colony (and the second such in the same area). In Breton, Cornouaille is known as Kernev or Bro-Gernev, and in Latin as Cornugallia or Cornubia. In Cornish, Kernev is written Kernow, but the pronunciation is the same.