Society in moral decline (7)
I believe the answer is:
descent
'decline' is the definition.
(I know that decline can be written as descent)
'society in moral' is the wordplay.
'society' becomes 's' (common abbreviation in names of organisations).
'in' means one lot of letters goes inside another.
'moral' becomes 'decent'.
's' put into 'decent' is 'DESCENT'.
(Other definitions for descent that I've seen before include "Derivation from an ancestor - going down" , "line" , "Ancestry - downward move" , "Roots" , "A climb down" .)