Hollow in a wall (6)
I believe the answer is:
recess
'hollow in a wall' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for recess that I've seen before include "bay" , "Alcove for remission of business" , "Enclosure set back or indented" , "break needed!" , "A niche or a temporary business break" .)