Britanni
The Celtic-speaking people of Great Britain were known as Brittanni in Latin and as Βρίττωνες in Greek. This name like Galli and Celtae ultimately derives from a tribal name, in this case that of the Priteni, recorded by Pytheas in the 4th century BC, apparently a self-designation of the people later known as Picts.
Read more about this topic: Names Of The Celts