As Brittānia from the 1st century B.C.E., from Ancient Greek Πρεττανία (Prettanía), used by Diodorus, earlier νῆσος (nêsos) Πρεττανική (Prettanikḗ) or Βρεττανίαι (Brettaníai), used by Pytheas (4th century B.C.E.) of the entire archipelago now known as the British Isles.
The Ancient Greek name is ultimately from a Celtic ethnonym, reconstructed as early Brythonic *Pritani, perhaps from a Proto-Celtic *Kʷritanī, *Kʷritenī, whence Welsh Prydyn (“Picts”), Old Irish Cruthne, Cru(i)then-túath (“Picts”), from Proto-Indo-European *kʷer- (“to do”).
Because Brittany (“Little Britain”) was settled at the end of the Roman era by migrants from Britain, the original descendants of Brittō often have the meaning "an inhabitant of Brittany", with a later reborrowing from Classical Latin being used to form the word for "an inhabitant of Great Britain".
- Asturian: bretón
- Catalan: bretó, britó
- English: Breton, Briton
- French: Breton
- Old Portuguese: breton
- Spanish: bretón
- → Proto-Brythonic: *Brɨθon (see there for further descendants)