Old servant disturbing a hidden man (10)
I believe the answer is:
handmaiden
'old servant' is the definition.
'handmaiden' can be an answer for 'servant' (handmaiden is a kind of servant). I am unsure of the 'old' bit.
'disturbing a hidden man' is the wordplay.
'disturbing' indicates an anagram (I've seen this in other clues).
'a'+'hidden'+'man'='ahiddenman'
'ahiddenman' is an anagram of 'HANDMAIDEN'.
Can you help me to learn more?
(Another definition for handmaiden that I've seen is " Female servant".)