Common Brittonic (Welsh: Brythoneg; Cornish: Brythonek; Breton: Predeneg), also known as British, Common Brythonic, or Proto-Brittonic, was a Celtic language spoken in Britain and Brittany.. It is a form of Insular Celtic, descended from Proto-Celtic, a theorized parent tongue that, by the first half of the first millennium BC, was diverging into separate dialects or languages.

Elmet (Welsh: Elfed), sometimes Elmed or Elmete, was an independent Brittonic kingdom between about the 5th century and early 7th century, in what later became the smaller area of the West Riding of Yorkshire then West Yorkshire, South Yorkshire and North Derbyshire.