Mordred: m The name of King Arthur's illegitimate son by his sister, Morgawse. The earliest form of the name is Medrawt,from Annals of Cambria,written in 10th century.
Possible meanings: Dread of the Sea- (welsh 'mor') ('mar');dred could possibly be Middle English form of 'dread'? ,Death- (French 'Morte'), Death-Cousel- (French 'Morte' and OE 'raed')
Those are just me brainstorming, I don't know whether any of those are correct ('cept where the name appears)...any other ideas though? I especially can't find much on 'Medrawt'...it also appears as "Medraut". I'm pretty sure it's Welsh though, like most beginnings of Arthurian stuff.