Sharp mountain ridge (5)
I believe the answer is:
arete
'sharp mountain ridge' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for arete that I've seen before include "feature of range" , "Glacial ridge" , "Narrow mountain ridge - eater (anag)" , "Sharp ridge on mountain, with a tree" , "part of mountain range" .)