Contrive to wipe out each unfinished city square (5)
I believe the answer is:
'square' is the definition.
'contrive to wipe out each unfinished city' is the wordplay.
I cannot quite understand how this works, but
'city' could be 'la' (Los Angeles) and 'la' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for plaza that I've seen before include "Public square for pedestrians" , "Hotel" , "Sp. square, market-place" , "Town square (Sp.)" , "Public square, as in Spanish town" .)