For those unfamiliar with Cornish, it is classed as a p-Celtic member of the family of Celtic languages, which was once spoken across much of Europe, and is now restricted to the insular world and Brittany: the only surviving languages being Cornish, Welsh and Breton (all p-Celtic), and Manx, Scots Gaelic and Irish (all q-Celtic).
The relationship between these two branches is illustrated by p-Celtic words such as peduar W and their q-Celtic equivalents: cethar [Ir].
The etymology, morphology, syntax and phonology of Cornish and the other Celtic languages ultimately derive from a putative proto-Indo European or proto-Celtic language or family of languages spoken in Britain in pre-history.
Cornish Onomastics is the study of onomastics (personal name data) and toponymics (place name data) in relation to Cornwall in the Early Medieval Period (350 CE to 1000 CE). These names are almost completely in the Cornish language (the Brittonic used in Cornwall and a relative of Welsh and Breton.
Sometime before C6 the closely related South-western British and Western British languages started to look less like Gaulish and more like the modern p-Celtic languages, and Cornish, Welsh, Breton and Cumbric (extinct) began taking shape as modern European languages. Cornish and Breton (from South-western British) eventually diverged from each other during the last part of the Early Medieval Period.
There will have been dialectic differences in these regions of Brittonic usage as well as differences in naming practice between them, but the structure and many name elements of Early Cornish personal names broadly follows that of early names found in Britain, Ireland, Gaul and Celt-Iberia. It is these names that have come down (with modification) to Cornish today including well known names such as Arthur, Gerent and Winwaloe.
Cornish is one of the oldest indigenous languages of Britain, with its roots stretching back thousands of years and to the first settlements of Britain (believed to be the Late Neolithic, when farming was established).