MORFUDD (standardized modern form)
Morfudd is the twin sister of Owein ap Urien Rheged, both said to be children of the otherworld-mother Modron. This would give her the same calculated date of ca. 530. Morfudd also makes a walk-on appearance in the tale of Culhwch and Olwen, while her brother Owein, in addition to numerous reasonably historic references, is inserted by Geoffrey of Monmouth into the Matter of Britain and eventually gets his own Arthurian romance, as Yvain.
Morud - JC MS 20 written late 14th c., copied from ms ca. 1200 (this is a slightly corrupted form)
Moruud - Peniarth Ms. 47
Morwyd - Peniarth Ms. 50
Moruyd - White Book of Rhydderch (fictional) (from Bromwich TYP)
Moruud - Red Book of Hergest (fictional) (from Bromwich TYP)
While this woman appears to be the only reliable early Morfudd (Bartrum WCD lists another who is purely legendary), the name is reasonably common in the later medieval period. The lack of early examples, however, makes historic reconstruction difficult.
If this name is understood as a typical dithematic compound, then the first element can be isolated fairly confidently as Mor-, an element that has two possible origins in Brythonic names: *Mori- "sea" and *Maro- "large, great". But by the mid 6th century, both of these would appear as Mor-.
Despite the appearance of f at the beginning of the second element in the standardized form of the name, early medieval examples alternate the more conservative u/v and the slightly later w, arguing for an underlying second element beginning with gw. (There are several names that show this same ambiguity, with apparent shifts in both directions from w to f and the reverse. See e.g. the discussion by Williams (1930) "Anawfedd, Blodeuwedd, -medd".)
This interpretation takes us back to an Old Welsh *guid for the second element, probably from Brittonic *ued-, for which we'd expect a mid 6th c. form vid. So for a mid 6th century Latinized written form, we can postulate Morvida, and a pronunciation along the lines of ['mor-wi"D] or, in English syllables, "MOHR-wi"dh" where i" represents a vowel like schwa but higher in the mouth, and "dh" represents the initial sound of "this".