Snare for retreating section (4)
I believe the answer is:
trap
'snare' is the definition.
(synonyms)
'retreating section' is the wordplay.
'retreating' shows that the letters should be reversed in order.
'section' becomes 'part' (synonyms).
'part' reversed gives 'TRAP'.
'for' acts as a link.
(Other definitions for trap that I've seen before include "Light horse-drawn carriage" , "Vehicle" , "website?" , "Trick" , "Part (anag.)" .)