The language is Cumbric, an offshoot of Welsh which was used until ~12th Century.
Helvellyn, when spoken correctly in proper Welsh (which was similar to the Cumbric language), sounds a lot like 'halltllyn' (ie pronounced in Welsh: Ha-cleckt-clin)
The Welsh word llyn (in Welsh pronounced klin) is Welsh for a lake.
The Welsh word 'hallt' (pronounced ha-klt) has many different meanings, including a hillside, cliff edge, severe, and salty.
Maybe over time Halltllyn mutated into Helvellyn, along with the English pronunciation rather than Cumbric/ Welsh. As Helvellyn is next to a small lake called Red Tarn, prehaps it means 'hillside next to a lake'.
Helvellyn is an unpopulated mountain. Not counting sheep!
It is claimed that two entities own Helvellyn. The east of Helvellyn is reported as being owned by Lake District National Park Authority. From the west of Helvellyn to Thirlmere is reported as being owned by United Utilities.
950 metres
~Mallory Prentiss
Enw. That is how you say name in Welsh.
Freddy Welsh's birth name is Fred A. Welsh.
Mikey Welsh's birth name is Michael Welsh.
It doesn't appear to be a Welsh name and would not have a Welsh version.
Helvellyn, Cumbria
Ronnie Welsh's birth name is Walter Ronald Welsh.
Susan Welsh's birth name is Welsh, Susan E..
The Welsh word for "Welsh" is Cymraeg :)