This opal's no good for institutions (9)
I believe the answer is:
hospitals
'institutions' is the definition.
(I have seen 'Medical institutions ' mean 'hospitals' so perhaps 'institutions' could also mean 'hospitals')
'this opal's no good' is the wordplay.
'no good' indicates an anagram (no good can mean faulty or defective).
'this'+'opals'='thisopals'
'thisopals' anagrammed gives 'HOSPITALS'.
'for' acts as a link.
(Other definitions for hospitals that I've seen before include "Lost aphis found in health centres" , "Medical institutions" , "Buildings with wards" , "Infirmaries" .)