Cedewain (or Cydewain) was a medieval cantref in the Kingdom of Powys. It possibly consisted of the commotes (cymydau) of Cynan, Hafren and Uwch Hanes. Other sources give the commotes as Cedewain, Eginlle and Ceri. It lay at the south of the kingdom, bordering with the cantrefi of Caereinion and Ystlyg to the north across the river Rhiw, and the cantrefi of Arwystli (subject to disputes between Powys and Gwynedd) and Maelienydd (originally an independent kingdom) to the south. Its easterly border, which was the River Severn, faced England.