Icelandic equivalent for "Devon":
"Devon" is derived from the toponym "Dumnonia", the region near Cornwalls, inhabited by the Dumnonii, which is thought to mean "deep valley dwellers" from proto Celtic *dubnos 'deep'. In the Brittonic, Devon is known as Welsh: Dyfnaint, Breton: Devnent and Cornish: Dewnens, each meaning "deep valleys." (source: English Wikipedia: Devon). "Dubnos" also means "dark" and is the root of the Nordicized Celtic name "Dufþakur". There's also the name Dufn(i)all, which is the Viking corruption of the original form of Donald, in which "Dufn", comes from Domn (world)
I would take "Dufn" as the root for derivations of the topnym "Devon"
Devon, Devonshire: Dufnskíri ("Skíri" old Icelandic borrowing from Anglo-Saxon, the equivalent of "shire")
Devonians (the cEltic tribe of the Dumnonii): Dufnungar , dufnverjar
Devonian (in geology): "Dufneska tímabilið", "Dufnöld", but combinations with "velskur" are aso possible. The Celtic people were called "welsh" (strangers) by the Anglo-Saxon invaders: "Dufnvelska tímabilið". The name is often called "the Age of Fish", because fish reached a large diversity during this era and the first ray-finned and lobe-finned bony fish appeared, so "frumfiskatímabilið" or "Fiskafrumöld" is also an option.
Devon (a feminine personal name): Dufný (Dufný, Dufný, Dubnýjar)
