On 12 Feb 2012 at 15:20, Christopher Gwinn wrote:

> > No. The Irish word looks to all intents and purposes like a compound
> > of so/u- "good" and cíall "sense, intelligence, mind"
> 
> Compare Welsh hybwyll, "thoughtful, discreet, prudent, sensible, prudent, wise".

Another possible morphological difference between W hybwyll and OIr. 
soichell occurred to me, even though strictly speaking it cannot be 
seen nor proved with the attested forms. Adjectival compounds with 
su/o- as first member are frequently i-stems in Irish, probably 
continuing an older morphological pattern: basis: o/ā-stem noun --> 
derivative: su/o- + i-stem adjective. W hybwyll could be such an 
adjective, but the stem class is entirely obliterated.

The determinative conpound soichell "liberality" (if < "good sense") 
has simply retained the stem class of the base noun, i.e. ā-stem 
inflection.

David