A run-down area welcoming closure of donkey sanctuary (6)
I believe the answer is:
asylum
'sanctuary' is the definition.
(synonyms)
'a run-down area welcoming closure of donkey' is the wordplay.
'run-down area' becomes 'slum' (I've seen this before).
'welcoming' is an insertion indicator (in sense of 'inviting in').
'closure of' indicates one should take the final letters.
The final letter of 'donkey' is 'y'.
'slum' placed around 'y' is 'sylum'.
'a'+'sylum'='ASYLUM'
(Other definitions for asylum that I've seen before include "Madhouse" , "Place of shelter or refuge" , "Place of safety or protection" , "Place of refuge, once a mental institution" , "Protection given to political refugee" .)