Been too taken with other things to read all of this thread, but
"duibheagán" has nothing to do with "aigéan", beyond its association
with the deeps, in fact it could have come from "doimheagán".
I'd recommend putting a random selection of words such as "leabhragán",
"taisceadán", "seastán" "sanasán", "malartán", "sporan", etc., into one
linguistic shopping trolly and posting the lot to list
[log in to unmask] (because "leabhragán" isn't an Old Irish
Not promising answers via [log in to unmask], but worth a try,
if you feel like it.
Difficult choice here: this being a free afternoon I promised myself, do
I switch off now to go work in the garden, or to dance again to Leonard
Cohen, having recently acquired a boxed set of his. Must do one or the
other, lest the worker in me find itself automatically translating his
"Future" into Irish!
Scríobh Dennis King:
> Fine, Seán. But that does not account one way or the other for the
> 17th cent. "duibheagán" < dubh + aigéan.