On Sun, 20 Mar 2016 21:06:15 -0700, Christopher Gwinn <[log in to unmask]> wrote:

>> I've been told the suffix -iawn or -ion was often added to personal
> names to give the name of a district ('territory of x') for example
>​> ​
>Cunedda's sons Ceretic, Abloyc, Etern, and Osmail are remembered
> in Ceredigion, Aflogyon, Edeyrnion, and Osmeliaun.
>​That seems to be the case in Wales, but of course Lleuddun was supposedly
>from what is now southern Scotland.

So are there other placenames in that part of the world that receive the -iawn or -ion treatment to indicate a wider district the way personal names did in Wales?

>The Proto-Celtic root *aidu- apparently did not survive in Brittonic; if
>​ ​
>it did, I think we would expect it to produce Welsh *oedd.
>> So Luguaidonas > Lleuoeddon then? And there's no way that would
>​> ​
>end up shortened to Lleuddun or something similar?
>​I highly doubt it. The cluster -euoedd- occurs in Welsh, for example in
>deuoedd and deheuoedd.
>- Chris Gwinn​

Thanks very helpful I appreciate the time. 

One last question: the examples you gave of that vowel cluster in Welsh are they both cases of modifying a shorter word with -oedd? 

deau > deheuoedd
dau > deuoedd

Does that necessarily mean that vowel cluster wouldn't be shortened in a different circumstance if it were only a leftover from phonological shifts from primitive to later forms of Welsh?