Rock shelf (5)
I believe the answer is:
ledge
'rock shelf' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ledge that I've seen before include "Surface under e.g. window" , "Mantelpiece" , "Ability to contain one's emotions" , "Submerged underwater shelf" , "Projecting shelf, horizontal projection" .)