Cynllaith or Cynllaeth (English: Early Milk) was a cwmwd (commote) of north east Wales in the cantref of Swydd y Waun which was once part of the Kingdom of Powys and later part of the smaller kingdom of Powys Fadog.
Cynllaith, or at least the part of it called Cynllaith Owain, was part of the inheritance of Owain Glyndŵr in 1370. The titles Baron of Glyndyfrdwy and Lord of Cynllaith Owain were used by the dispossessed former ruling family of Powys Fadog before Owain was proclaimed Prince of Wales in 1400.
- Jones, John (1824). The History of Wales. London: J Williams. p. 105.
- Rees, William (1951). An Historical Atlas of Wales from Early to Modern Times. Faber & Faber.
- Rees, William (1937). "The Union of England and Wales". Transactions of the Honourable Society of Cymmrodorion: 88.
- "Owain Glyndwr". Castle Wales.
- "OWAIN GLYNDWR". Dictionary of Welsh Biography. National Library of Wales.