Sophisticated worldliness shown by metropolitan leader departing from large town (8)
I believe the answer is:
urbanity
'large town' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'sophisticated worldliness shown by metropolitan leader departing from' is the wordplay.
'sophisticated worldliness' becomes 'it' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'shown by' means one lot of letters go next to another.
'metropolitan' becomes 'urban' (I've seen this in another clue).
'leader departing' means to remove the first letter.
'from' becomes 'by' (by can mean from a particular person).
'by' with its first letter taken away is 'y'.
'it' put after 'urban' is 'urbanit'.
'urbanit'+'y'='URBANITY'
Can you help me to learn more?
(Other definitions for urbanity that I've seen before include "Elegance and sophistication - of city dweller?" , "Suave, polished manner" , "Suave nature" , "showing sophistication" , "Refined quality - but rainy (anag)" .)