ENYNNY (standardized modern form)
In the same generation as Urien and Efrddyl, also described as a daughter of Cynfarch Oer, but with no identification of the mother, is Enynny, the mother of Meurig, who figures in the Life of Saint Cadog. There is a certain amount of difficulty in reconciling the dates and geography involved. The events involving Cadog are located around Gwynllwg in the south-east of Wales -- although the re-location from the North might reasonably be explained by a marriage. Bartrum (WCD) assigns Cadog a date ca. 495 (and his Life mentions enough historic personages that he may be considered reasonably pinned down) and Meurig a questionable date ca. 470 although it isn't at all clear what this calculation is based on. Assuming Enynny is accurately identified as a sister of Urien Rheged, that gives her a date ca. 500, and while Meurig's father is mysteriously absent from most references to him, in at least one place he is identified as Caradog Freichfras, who is assigned a calculated date ca. 470. The most likely explanation is that multiple people have been conflated in some fashion here, but sorting them out is probably impossible. It appears that all the information about the name Enynny comes via the S. Cadog connection, so even if this is a different woman than the possible northern woman, it is the evidence we must examine. (Bartrum WCD & EWGT)
Enhinti Life of S. Cadog (Cotton Ms. Vespasian A xiv (ca. 1200), written ca. 1100)
Enynny (Peniarth Ms. 131, ca. 1475; other versions of this text have less reliable forms such as Efynny Cardiff Ms. 25 1640; Enyni Peniarth Ms. 131 before 1547)
a mis-copied form can be seen in:
Emminni JC Ms. 20 written late 14th c., copied from ms ca. 1200
and we can safely ignore the very corrupt, later forms:
Henfyn (Harleian Ms. 2414 fo. 59v; Mostyn 212b p.59, both late 16th c.)
With the exception of the possible conflation of more than one woman of the name here, I know of no other examples of this name.
The profusion of forms for this name is less of a problem for reconstruction than some inherent ambiguities. Both nh and nt appear in Old and Medieval Welsh for original *nt (the precise nature of the sound could depend on various positional factors, so the appearance of both in Enhinti need not be a problem). Borrowings into English in the 6th century show that the pronunciation of *nt was still firmly [nt] at this time. However nh could also derive from nVs if the s began the second element of a compound (Jackson p.514), and this h would have been lost by late Medieval Welsh, just as one deriving from nt would. So we can set up two avenues to explore:
_nt_nt_ (with the underscores filled in by vowels)
This s at the beginning of second elements shifted to being pronounced [h] and written h probably some time during the first half of the 6th century, and direct evidence is lacking for the date of this woman's life. So even if we lean towards that explanation, we're still left with uncertainty about the expected forms at our desired date.
The initial vowel has many of the same problems as that of Efrddyl -- by the 7th century we could assume that it has assumed the form e, but before that we have a number of possible origins. The other vowels seem likely to be original, but there must have been some entire syllable lost at the end in order to preserve the final vowel (i.e., we aren't dealing with an original -ntia losing an inflectional ending, but rather with an original -nti_a with the space filled with a consonant or semi-vowel). One possibility here would be -ntiga, and another might be -ntiia (= [-ntija]), but there may be other possibilities as well.
If etymological connections could be made with other names, it might be possible to narrow down the suggestions here, but as it stands, they multiply too rapidly to be manageable. After the syllable loss and sound-shifts leading up to the 7th century, it would be reasonable to suggest Entintia or Enhintia as a Latinate written form, and ['En-hIn-hi] as a pronunciation (or, in English syllables, "EN-hinn-hee"), whatever the origins. But I will decline to try a form earlier than the 7th century.