From Wiktionary, the free dictionary
From over- + kingdom.
overkingdom (plural overkingdoms)
- A unit, composed of several kingdoms, presided over by an overking.
1922, John Ryan, Ireland from A.D. 800 to A.D. 1600, Browne and Nolan, page 282:The overkingdom of Airgialla comprising Armagh, Monaghan, parts of Louth, Fermanagh, and Tyrone, had ceased to be when the Book of Rights was compiled.
