Gentleman's abrupt personal assistant (3)
I believe the answer is:
sir
'gentleman's' is the definition.
(a man may be addressed as sir)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for sir that I've seen before include "... ___ John Major" , "Male title of respect" , "Poet and novelist" , "Title for knight or teacher" , "Form of address for a knight" .)