Confidential, secret (7)
I believe the answer is:
private
I believe this is a double definition.
'confidential' is the first definition.
(similar in meaning)
'secret' is the second definition.
(similar in meaning)
(Other definitions for private that I've seen before include "Army rank; secluded" , "One's own" , "Rank, concealed" , "'Saving - - Ryan' (film)" , "Personal or secret" .)