The end of an alphabet (5)
I believe the answer is:
omega
'the end of an alphabet' is the definition.
(I've seen this in another clue)
'of an alphabet' is the wordplay.
'of' becomes 'o''.
'an alphabet' becomes 'mega' (I can't explain this - if you can you should give a lot more credence to this answer).
'o'+'mega'='OMEGA'
Can you help me to learn more?
(Other definitions for omega that I've seen before include "character in Greek literature?" , "in Greece, the limit!" , "Conclusion" , "Final Greek letter" , "Last thing" .)