Aside from those academies, this is the top one (4)
I believe the answer is:
acme
'aside from those academies this is the top one' is the definition.
'acme' can be an answer for 'is the top' (I've seen this in another clue). I'm not sure about the rest of the definition.
'top one' is the wordplay.
'top' becomes 'ac' (I can't justify this - if you can you should give a lot more credence to this answer).
'one' becomes 'me' (a setter might use 'one' to humourously mean 'me').
'ac'+'me'='ACME'
Can you help me to learn more?
(Other definitions for acme that I've seen before include "High point of excellence" , "crisis in history" , "Aim of mountaineers" , "Peak of perfection" , "Height of perfection" .)