Shelf, sill (5)
I believe the answer is:
ledge
I believe this is a double definition.
'shelf' is the first definition.
(I know that shelf can be written as ledge)
'sill' is the second definition.
(I've seen this in another clue)
(Other definitions for ledge that I've seen before include "Projecting shelf, horizontal projection" , "Mantelpiece" , "Shelf-like projection" , "Submerged underwater shelf" , "Ability to contain one's emotions" .)