A hollow in a wall (5)
I believe the answer is:
niche
'a hollow in a wall' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for niche that I've seen before include "Well-suited position" , "Specialised corner of the market" , "Specialized market" , "Suitable spot" , "Position well suited to the occupier" .)