What is the X in X-mas?
fem. proper name, from Medieval Latin, from Old High German Ida, perhaps related to Old Norse ið "work."
first recorded king of Bernicia (from 547), soon after the foundation of the kingdom of Bernicia by the Angles in the British Isles. He supposedly built the fortress of Bebbanburh, the modern Bamborough; and after his death his kingdom, which did not extend south of the River Tees, reportedly passed to his sons