Conceal a confidential note (7)
I believe the answer is:
secrete
'conceal' is the definition.
(I know that secrete is a more specific form of the action conceal)
'a confidential note' is the wordplay.
'a confidential' becomes 'secret' (I've seen this in another clue).
'note' becomes 'e' (musical note).
'secret'+'e'='SECRETE'
(Other definitions for secrete that I've seen before include "Hide away" , "(Of gland) produce (a substance)" , "Hold and send out substance into the body as gland does" , "Hide - discharge" , "Form substance for use within body, as liver does bile" .)