Shelf under the window looks almost foolish (4)
I believe the answer is:
sill
'shelf' is the definition.
(I've seen this before)
'almost foolish' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'foolish' becomes 'silly' (similar in meaning).
'silly' with its final letter removed is 'SILL'.
'under the window looks' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sill that I've seen before include "Mass of rock" , "Underwater rock ledge" , "Ledge beneath a window" , "Horizontal intrusion of igneous rock between sedimentaries, as in much of Hadrian's Wall" , "Window edge" .)