Robin's home in run-down estate (4)
I believe the answer is:
nest
'robin's home' is the definition.
(I've seen this before)
'in run-down estate' is the wordplay.
'in' indicates a hidden word.
'NEST' can be found hidden inside 'run down estate'.
(Other definitions for nest that I've seen before include "home for 22d [VIPERS]" , "Sent to bird's home" , "Snug retreat" , "Bird's house" , "Bird shelter" .)