Big city's sole import is affected (10)
I believe the answer is:
metropolis
'big city's' is the definition.
(I've seen this before)
'sole import is affected' is the wordplay.
'is affected' is an anagram indicator.
'sole'+'import'='soleimport'
'soleimport' anagrammed gives 'METROPOLIS'.
(Other definitions for metropolis that I've seen before include "Big city" , "capital" , "chief centre" , "centre of activity" , "population centre" .)