Bretwalda

Bretwalda (also brytenwalda and bretenanwealda, sometimes capitalized) is an Old English word the first record of which comes from the late 9th century Anglo-Saxon Chronicle. It is given to some of the rulers of Anglo-Saxon kingdoms from the 5th century onwards who had achieved overlordship of some or all of the other Anglo-Saxon kingdoms. It is unclear whether the word dates back to the 5th century and was used by the kings themselves, or whether it is a later, 9th-century, invention. The term bretwalda also appears in a 10th-century charter of Æthelstan. The literal meaning of the word is disputed, and may translate to either 'wide-ruler' or 'Britain-ruler'.

The rulers of Mercia were generally the most powerful of the Anglo-Saxon kings from the mid-7th to the early 9th centuries, but are not accorded the title of bretwalda by the Chronicle, which had an anti-Mercian bias. The Annals of Wales continued to recognise the kings of Northumbria as "Kings of the Saxons" until the death of Osred I of Northumbria in 716.

The first syllable of the term bretwalda may be related to Briton or Britain. The second element is taken to mean 'ruler' or 'sovereign', though is more literally 'wielder'. Thus, this interpretation would mean 'sovereign of Britain' or 'wielder of Britain'. The word may be a compound containing the Old English adjective brytten (from the verb breotan meaning 'to break' or 'to disperse'), an element also found in the terms bryten rice ('kingdom'), bryten-grund ('the wide expanse of the earth') and bryten cyning ('king whose authority was widely extended'). Though the origin is ambiguous, the draughtsman of the charter issued by Æthelstan used the term in a way that can only mean 'wide-ruler'.

...
Wikipedia