Unnamed fell runner (3)
I believe the answer is:
ski
This might be a double definition.
'unnamed fell' is the first definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'runner' is the second definition.
(something which 'runs', ie moves quickly on snow)
(Other definitions for ski that I've seen before include "Winter sport item" , "Glide ove snow" , "Winter-sports item" , "Take part in a winter sport" , "Snow blade" .)