Seems nobody knows, as this site says (following the link
Arwel).
Some sites that I found with Google give a meaning of 'prominent', but as it is often the case, this may be simply made-up. The Welsh dictionary at
http://www.cs.cf.ac.uk/fun/welsh/LexiconForms.htmlknows nothing of a word 'arwel' and translates English words like 'prominent' or 'famous' into quite different Welsh words.
Rene www.BabyNames.ch