Finally settled in French Society, formerly in diplomatic corps (9)
I believe the answer is:
ensconced
'finally settled' is the definition.
'ensconced' can be an answer for 'settled' (I've seen this before). I'm unsure of the 'finally' bit.
'in french society formerly in diplomatic corps' is the wordplay.
'in french' becomes 'en' ('in' in French).
'society' becomes 's' (common abbreviation in names of organisations).
'formerly' becomes 'once' (synonyms).
'in' indicates putting letters inside.
'diplomatic corps' becomes 'cd' (I can't explain this - if you can you should believe this answer much more).
'once' put within 'cd' is 'conced'.
'en'+'s'+'conced'='ENSCONCED'
Can you help me to learn more?
(Other definitions for ensconced that I've seen before include "Installed" , "in safe seat" , "Settled comfortably" , "Safely established" .)