From Alan James – 19 July 2020
It’s probably no help at all, but Carnellan is on record as a Cornish surname, probably from a place-name, though not in Oliver Padel’s Cornish PN Elements. He mentions Carnello x2, but gives no opinion on the 2nd element, and the first could be carn or corn. Bannister’s 1871 Glossary of Cornish Names, where I found it online, suggests ‘elm?’ That would be elowen, not paralleled in Welsh; C elen, W elain, ‘fawn’ might be more plausible. I don’t find anything remotely similar in Archif Melville RIchards, but W cornelyn ‘small corner’ might just be in the picture. Suffice to say, it might just possibly be Brittonic. But without more earlier/ varied forms and/or any idea where it was, we’re entirely in the fog.
Still, thanks for the additional reference David!