Dennis, many thanks for your help!
> "Dúnad" generally means a temporary encampment, as of an army
> on campaign, pretty much equivalent to "longphort". This last
> word is a bit odd, however, in that it looks like a compound
> of "long" (ship) and "port" (place < Lat. "portus" = port).
> But it never seems to mean "ship port = harbour"! Can someone
> explain that?
When researching the history of Dublin, I actually came across a
reference to longphorts described as viking defended ship harbours. The
ref was to P129 of:
Fitzhugh, William. W. and Ward, Elisabeth I., eds. Vikings: The North
Atlantic Saga. (WA: Smithsonian Institute Press, 2000.)
I don't have the book, so I can't comment further on it.
Apparently they are also described as 'defended harbours' in
O'Corrain, D: Ireland before the Normans. p90.