>> A lot of ancient British words are really pidgin Latin and so "cwn" is clearly from the Latin "canis".

I'm not sure about that one. The Gaelic (probably related to the Brythonic) for hound is <b>cu</b> (as in Cu Chulainn = Hound of Cullen).

Culllen itself has <b>cu</b> roots and places like Glencullen & Kilcullen are all dog related.