What is the X in X-mas?
Anglo-French Bretun, from Latin Brittonem (nominative Britto, misspelled Brito in MSS) "a member of the tribe of the Britons," from *Britt-os, the Celtic name of the Celtic inhabitants of Britain and southern Scotland before the 5c. Anglo-Saxon invasion drove them into Wales, Cornwall, and a few other corners. In 4c. B.C.E. Greek they are recorded as Prittanoi, which is said to mean "tattooed people." Exclusively in historical use after Old English period; revived when James I was proclaimed King of Great Britain in 1604, and made official at the union of England and Scotland in 1707.