Dindaethwy

Coordinates: 53°15′29″N 4°07′48″W / 53.258°N 4.130°W / 53.258; -4.130

Dindaethwy or Tyndaethwy was a commote of cantref Mon in medieval Gwynedd. Its maerdref and seat of local governance was Llanfaes near modern Beaumaris on the Menai Strait. Llanfaes, Llanvaes or Llanmaes was such an important port that the cantref itself was often called by its name.

The first element of the name may involve a reference to the hillfort Bwrdd Arthur in the former parish of Llanfihangel Din Sylwy. King Cynan of Gwynedd had his principal court at Llanfaes, for which he became known as "Cynan Dindaethwy".