Disclosure about Royal Society is a setback (8)
I believe the answer is:
reversal
'setback' is the definition.
(synonyms)
'disclosure about royal society' is the wordplay.
'disclosure' becomes 'reveal' (I have seen 'Final disclosure' mean 'reveal' so perhaps 'disclosure' could also mean 'reveal').
'about' indicates putting letters inside.
'royal society' becomes 'RS'.
'reveal' placed around 'rs' is 'REVERSAL'.
'is a' acts as a link.
(Other definitions for reversal that I've seen before include "A set-back or backwards movement" , "U-turn" , "switch" , "that doesn't affect mum or dad" , "Volte-face" .)