Waun-oer is a mountain in Snowdonia, North Wales, situated approximately four miles to the south-west of Aran Fawddwy. It is one of the peaks in the Dyfi hills, a subgroup of the Cadair Idris group. It is a top of Maesglase and the summit consists of a trig point that crowns an uneven grassy plateau. It is connected to Cribin Fawr to the east.