Let it be known though it's confidential (8)
I believe the answer is:
intimate
'confidential' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for intimate that I've seen before include "Friendly" , "Suggest to trusted friend?" , "Personal - hint - friend" , "Make known" , "Hint to a familiar friend" .)