Northumbria Syllabification: (North·um·bri·a)Pronunciation: /nôrˈTHəmbrēə/Definition of Northumbria an area of northeastern England. an ancient Anglo-Saxon kingdom in northeastern England that extends from the Humber Estuary to the Forth River. Derivatives Northumbrian adjective & noun Origin:from obsolete Northumber, denoting a person living beyond the HumberNorthumbria in other Oxford dictionaries Definition of Northumbria in the British & World English dictionary