Private servant (6)
I believe the answer is:
batman
'private servant' is the definition.
'batman' can be an answer for 'servant' (I've seen this before). I'm not sure about the 'private' bit.
'private servant' is the wordplay.
'private' becomes 'bat' (I can't explain this - if you can you should believe this answer much more).
'servant' becomes 'man' (man is a kind of servant).
'bat'+'man'='BATMAN'
Can you help me to learn more?
(Other definitions for batman that I've seen before include "Cartoon hero of Gotham City" , "Superhero - Turkish province and city" , "gives help to one in a mess?" , "Caped superhero" , "cartoon character" .)