Master, teacher holding me back (5)
I believe the answer is:
demon
'master' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'teacher holding me back' is the wordplay.
'teacher' becomes 'don' (don is a kind of teacher).
'holding' means one lot of letters goes inside another.
'back' says the letters should be written in reverse.
'me' back-to-front is 'em'.
'don' enclosing 'em' is 'DEMON'.
Can you help me to learn more?
(Other definitions for demon that I've seen before include "ace" , "Inspiring force" , "Evil spirit, devil" , "Monster" , "Bad spirit" .)