Crossword Genius

Secret family decree in advance (11)

Ross

I believe the answer is:

clandestine

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'secret' is the definition.
(synonyms)

'family decree in advance' is the wordplay.
'family' becomes 'clan' (clan can mean a large family).
'decree in advance' becomes 'destine' (I can't justify this - if you can you should give a lot more credence to this answer).
'clan'+'destine'='CLANDESTINE'

Can you help me to learn more?

(Other definitions for clandestine that I've seen before include "Concealed" , "Send a client (anag) - covert" , "Done secretively" , "through the backdoor" , "Private" .)

I've seen this clue in The Guardian.
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