Concrete section (4)
I believe the answer is:
slab
'concrete section' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slab that I've seen before include "Hunk" , "Thick piece of something" , "Thick flat piece of stone" , "Piece, e.g. of cake" , "Paving stone" .)