a member of the Brythonic group of Celtic languages. Spoken in Cornwall in southwestern Britain, it became extinct in the 18th or early 19th century as a result of displacement by English (English language) but was revived in the 20th century. Cornish is most closely related to Breton (Breton language), the Celtic language of Brittany in northwestern France.

Cornish was strongly influenced by English even in medieval times, and later its orthography and vocabulary showed many English elements. By 1600 it was spoken only in the farthest western part of Cornwall, and by 1800, or shortly thereafter, it had no speakers at all. Modern revivalists constructed a “unified Cornish” in the early 20th century. At the turn of the 21st century the population of Cornish speakers remained small, numbering perhaps 300, but the language showed signs of renewed vigour with the creation of a standard written form in 2008.