... the name of the valley which extends from Bedd Gelert in the direction of Pen y Gwrd... The correct pronunciation, according to the Gwyndodeg or Venedotian dialect, is Nangwynan, but the spelling Nanhoenem in an old charter cited at page 198 of this volume seems to point to an original Nanhoenein, and this seems borne out in the same by Bryngwynem and Hendrefwynein.  So the personal name involved would now be Gwynain; and Nanhwynain sometimes occurs in that form.  But it is characteristic of the Gwyndodeg that it makes both ein and en in such positions into an: hence the correct Gwynedd pronunciation is Nangwynan, Bryn Gwynan, etc., while the spellings Nanhwynen and Bryn Gwynen occupy a sort of intermediate position between the local pronunciation and the book forms in ain.  There are reasons to suppose that the Gwyndodic predilection for a broad a in the ending of words is of no recent origin.  In fact, we seem to have the name Gwynein or Gwynain as Gwynhan in the ancient story of Culhwch ac Olwen in the Red Book of Hergest:  I refer to the designation therein of a certain Teithi Hen mab Gwynhan.  As I have said, Nangwynain and Bryn Gwynain have to be regarded as the book forms, and Nangwynan and Bryn Gwynan as the local forms; but Nant Gwynant and Bryn Gwynant are monstrosities of modern origin, partly due to the difference between Nanh-Wynan and Bryn Gwynan.  The explanation, however, of that difference is a very simple matter of Welsh grammar:  nant is feminine in the dialect, and so requires Gwynan to become Wynan; moreover, nt is changed into nh, as in fy nhad, "my father," for myn + tad.  In modern Welsh there is a tendency to efface the mutations and restore the radical consonants, whence Nanhwynan is made into Nant Gwynan.  This, however, is a very different matter from making the personal name Gwynan into Gwynant, as if it meant some sort of a nant, "brook or valley."  I have been told that Gwynant only dates from the time when an English settler built the house of Plas Gwynant, and what happened, I fancy, was this:  the new comer wanted a name for his house, and he was advised to consult the philological oracle of the neighbourhood, who without any hesitation gave sage reasons why Gwynan must be a corruption of Gwynant:  hence Plas Gwynant, and from the Plas the heresy has proceeded to attack Nanhwynan, Bryn Gwynan, and all the others involving the name of Gwynan... (Bedd Gelert: Its Facts, Fairies, & Folk-lore, Jenkins, 1899).