From: Old-Irish-L <[log in to unmask]> On Behalf Of Christopher Gwinn
> The DIL tentatively regards the io-stem cethrae "animals, cattle, flocks, herds" as a plural of cethir;
Yes, I said before that a certain number of attestations that are now included under "cethrae" could actually be plurals of "cethir". But IIRC, there are a few authentic examples of "cethrae" that cannot be so explained. In any case, a i̯o- or i̯ā-stem collective beside simple "cethir" is a very common pairing in Old Irish.
> if this is true, can it be cognate with Gaulish petuarios, Old Breton petguare, Welsh pedwerydd / pedwaredd "fourth"?
Formally, the comparison of cethrae with those words is possible, but semantically it doesn't make much sense. I would rather suspect that they would be independent, but formally coinciding formations.