Conceal confidential note (7)
I believe the answer is:
secrete
'conceal' is the definition.
(thesaurus)
'confidential note' is the wordplay.
'confidential' becomes 'secret' ('secret' can be a synonym of 'confidential').
'note' becomes 'e' (musical note**).
'secret'+'e'='SECRETE'
(Other definitions for secrete that I've seen before include "harbour" , "Hide - discharge" , "Place out of sight, hide" , "Cache" , "squirrel" .)