Crossword Genius

Cryptic from some clever expert, being extremely selective (6)

Ross

I believe the answer is:

secret

'cryptic' is the definition.
(synonyms)

I don't understand how the rest of the clue works.

(Other definitions for secret that I've seen before include "Private, or something private" , "Not public" , "Security classification level" , "It's not to be told" , "Kept under wraps" .)

I've seen this clue in The Guardian.
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