Cynllibiwg was evidently a place name

Toponymy

Toponymy is the scientific study of place names , their origins, meanings, use and typology. The word "toponymy" is derived from the Greek words tópos and ónoma . Toponymy is itself a branch of onomastics, the study of names of all kinds...

 in early medieval Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

.

The earliest surviving reference to it is in the Historia Brittonum, which describes a marvelous spring in the regione of Cinlipiuc that has an abundance of fish despite not being fed by a stream. John Edward Lloyd

John Edward Lloyd

Sir John Edward Lloyd , was a Welsh historian, the author of the first serious history of the country's formative years, A History of Wales from the Earliest Times to the Edwardian Conquest, 2 vols...

 notes that this Cinlipiuc appears to be one of the various district names created by adding the element -wg to a personal name, in this case an unknown Cunalipi or Cynllib. The Domesday Book

Domesday Book

Domesday Book , now held at The National Archives, Kew, Richmond upon Thames in South West London, is the record of the great survey of much of England and parts of Wales completed in 1086...

refers to a place called Calcebuef, which rendered ten shilling

Shilling

The shilling is a unit of currency used in some current and former British Commonwealth countries. The word shilling comes from scilling, an accounting term that dates back to Anglo-Saxon times where it was deemed to be the value of a cow in Kent or a sheep elsewhere. The word is thought to derive...

s; one editor suggests this is a corruption of Cynllibiwg and that it derives ultimately from the name of Saint Cynllo

Cynllo

Saint Cynllo is a British saint, who lived in the late 5th and early 6th centuries. His feast day is 17 July.He is variously described in the genealogical Bonedd y Saint as a brother of Saint Teilo or a grandson of Coel Hen...

. However, Lloyd connects this name instead to the cantref of Buellt. The Red Book of the Exchequer

Red Book of the Exchequer

The Red Book of the Exchequer is a 13th-century manuscript compilation of the records of the English Exchequer. Made of vellum, the book was compiled by a royal clerk who died in 1246...

, a mainly 13th-century compilation, mentions a region of seven cantrefs between the Severn

River Severn

The River Severn is the longest river in Great Britain, at about , but the second longest on the British Isles, behind the River Shannon. It rises at an altitude of on Plynlimon, Ceredigion near Llanidloes, Powys, in the Cambrian Mountains of mid Wales...

 and the Wye

River Wye

The River Wye is the fifth-longest river in the UK and for parts of its length forms part of the border between England and Wales. It is important for nature conservation and recreation.-Description:...

 that had been known as Kenthlebiac during the time of Rhys ab Owain

Rhys ab Owain

Rhys ab Owain was a king of Deheubarth in southern Wales.Rhys was the son of Owain ab Edwin of the line of Hywel Dda, and member of the Dinefwr dynasty. He followed his brother Maredudd as king of Deheubarth in 1072...

 of Deheubarth (died 1078). This would place Cynllibiwg in the region later known as Rhwng Gwy a Hafren

Rhwng Gwy a Hafren

Rhwng Gwy a Hafren was a region of medieval Wales, located in the Welsh Marches between Powys to the north and Brycheiniog to the south. It was bounded by the rivers Wye and Severn , hence its name. It covered approximately the same territory as Radnorshire, now part of the county of Powys...

, but reveals nothing about its extent and nature. The editor suggests that seven cantrefs should amended to three, perhaps Arwystli

Arwystli

Arwystli was a cantref in medieval Wales, located in the headland of the River Severn in what is now the county of Powys. It was chiefly associated with the Kingdom of Powys, but was heavily disputed between Powys, Gwynedd, and the Norman Marcher Lords for hundreds of years, and was the scene of...

, Maelienydd

Maelienydd

Maelienydd, sometimes spelt Maeliennydd, was a cantref and lordship in east central Wales covering the area from the River Teme to Radnor Forest and the area around Llandrindod Wells. The area, which is mainly upland, is now in Powys...

, and Elfael

Elfael

Elfael was one of a number of Welsh kingdoms occupying the region between the River Wye and river Severn, known as Rhwng Gwy a Hafren, in the early Middle Ages. Later in the Middle Ages it became a cantref. After the Laws in Wales Act of 1535, it became part of the new county of Radnorshire. ...

; these are mentioned earlier in the list as part of Powys in the time of 'Meic Menbis', but no longer such.

It has been postulated as an early kingdom, but is not accepted as such by the great majority of historians.