Alef (AYL-eff, but I'm guessing this pron.) - a king from Cornwall; name may be a form of the Viking name Olaf
Ainéislis (a-NAYCE-lish; "nayce" rhyming with "grace") - thought to come from a Celtic form of Stanislaus
Ardán (AR-dawn) - borne in Irish legend by one of those who accompanied Deirdre to Scotland, so she would not be forced to marry Conchubhar
Auryn (AW-rin - pr'd like Lauryn minus the L) - A derivative of Welsh aur, "gold"
Austell (AW-stell) - occurs in the medival "Life of St Mewan"; Austell was the Cornish godson of Mewan
Bradán (BRAD-awn) - from Gaelic bradán, "salmon"
Brannagh (BRAN-a) - as a male name, an anglicisation of Irish Breathnach, "Welshman")
Brannoc(k) (BRAN-nock) - compound of bran + ieuanc, so meaning "young raven"; Brannoc was a priest in 6th-C Cornwall
Brecon (BRECK-un) - Of Welsh/Cornish origin, but meaning uncertain
Cael ("cale") - From Irish caol, "slender"
Camber (KAM-bur) - Camber was the son of Brutus and supposedly the found of Wales (Cymru)
Canice (KAN-iss) - from Gaelic coinneach, "attractive person"; originally used for both genders but best known as that of a 6th-C Irish missionary priest Coinneach, so more common on males after that
Cathmore (KATH-more) - Irish: comes from cath + mór, meaning "great battle"
Ferris (FEH-riss) - probably from Phiarais, a Gaelic form of the norman name Piers (see Peter)
Gael ("gale") - Breton in origin: probably come from gaedheal, meaning "Irish"
Gethen (GETH-in) - comes from Welsh cethin, meaning "swarthy" or "fierce"
Maxen (MAKS-in) - a Welsh version of Magnus