Officer at the back (4,7)
I believe the answer is:
rear admiral
'officer at the back' is the definition.
I can't tell whether this defines the answer.
'officer at the back' is the wordplay.
'officer' becomes 'admiral' (admiral is a kind of officer).
'at' says to put letters next to each other (I've seen this in other clues).
'the back' becomes 'rear' ('rear' can be a synonym of 'back').
'admiral' put after 'rear' is 'REAR-ADMIRAL'.
Can you help me to learn more?
(Other definitions for rear admiral that I've seen before include "Naval officer" , "Naval rank above commodore" , "navy bigwig" , "Top brass" .)