The name of the city of York has changed from Eboracum (Celtic as recorded by Romans) to Eoforwic (Anglo-Saxon), Jorvik (Norse) and subsequently York. Welsh more closely conserves the original Celtic name :)
Brilliant, that answers a question I posted in a different comments section concerning this word
I almost wrote "new dress" as the translation ("ffrog" means dress in Welsh) but then I realised. Facepalm
Should it be Efrog Newydd with a capital letter? If not, I'd be very intrigued to find out why!