Weed in derelict area (4)
I believe the answer is:
tare
'weed' is the definition.
(I've seen this before)
'in derelict area' is the wordplay.
'in' indicates a hidden word.
'TARE' is hidden within 'derelict area'.
(Other definitions for tare that I've seen before include "Vetch plant" , "Vehicle's empty weight" , "Weight of container makes a vetch" , "Vessel's weight" , "Weight of unloaded vehicle" .)