Celtic Britons and the settlers in Brittany spoke a common language, which later evolved into Breton, Welsh and Cornish.

[3] 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 Anaweten, bishop of Saint-Corentin at Quimper Cathedral, took over Cornugallensis under the order of Nominoe, Duke of Brittany and Tad ar Vro.

The first element is from the name of a Brythonic tribe Latinized as Cornovii, meaning 'peninsula people', from the Celtic kernou, 'horn, headland', from PIE *ker- 'uppermost part of the body, head, horn, top, summit'.

Walh is an element found in the words and names walnut, Walloon, Wales, Wallasey, Waleswood, Wallachia, Wallace, Walcheren, and Walsh.

The existence of an ancient district in Anjou called "la Cornuaille" has led to the hypothesis that Cornouaille may have been a geographical or military label for all of southern Brittany as far as the northern shore of Domnonée in the 6th or 7th century.[speculation?]