The Boys' Brigade Mountaineering Club

Carnedd Dafydd is the 4th highest peak in Wales. It has a flat boulder-strewn summit with extensive precipitous crags (popular with rock and ice climbers) called Ysgolion Duon (The Black Ladders) to the north of its east ridge. It boasts an excellent and unfrequented Grade 1 scramble up to its northern ridge from Cwm Llafar (Resonant Valley), known as the Llech Ddu (Black Slate) Spur or sometimes Grib Lem (Corner Ridge).

See its entries on Walkhighlands or Wikipedia or view it from above on Google Earth.

Carnedd is a Welsh word that can mean Cairn, Tumulus, Mound, Heap, Pile or Ruin. In the context of a mountain name, the best translation would be Cairn.

Dafydd is a personal name. It is Welsh for David. Given that the adjacent peak is called Carnedd Llewelyn, the Dafydd referred to is likely to be Dafydd ap Gruffudd whose elder brother was Llywelyn ap Gruffudd (ap in Welsh means son of, equlivant to the Gaelic Mac or Irish O'). After his brother Llywelyn was killed in 1282, he succeded him as Prince of Wales, but had to go into hiding. He was captured by the English near Bera Mawr (Big Heap) in the northern Carneddau and was hanged, drawn and quartered at Shrewsbury in 1283.

An alternative theory is that Carnedd Llewelyn and Carnedd Dafydd are named after two successive Princes of Gwynedd: Llywelyn ap Iorwerth, also known as Llywelyn Fawr (Llewelyn The Great) and his son Dafydd ap Llywelyn, who was the first Welsh prince to claim the title Prince of Wales. See Virtual History for details

There is no concept similar to an apostrophe s in Welsh. Possession is indicated by juxtaposition. So, Carnedd Dafydd is translated as Dafydd's Cairn or David's Cairn.