Emperor in north cut off, retreating after a long time (8)
I believe the answer is:
napoleon
'emperor' is the definition.
(Napoleon is an example)
'in north cut off retreating after a long time' is the wordplay.
'in north' becomes 'na' (I can't explain this - if you can you should give a lot more credence to this answer).
'cut off' becomes 'lop' (I've seen this before).
'retreating' is a reversal indicator.
'after' is a charade indicator (letters next to each other).
'a long time' becomes 'eon' (eon is a kind of long time).
'lop' written backwards gives 'pol'.
'na'+'pol'+'eon'='NAPOLEON'
Can you help me to learn more?
(Other definitions for napoleon that I've seen before include "Frenchman known as The Little Corporal" , "In France, former sovereign" , "French VIP" , "Old French coin" , "Emperor - brandy" .)