Large conurbations (6)
I believe the answer is:
cities
'large conurbations' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cities that I've seen before include "Dickens novel, 'A Tale of Two ......'" , "urban centres" , "Densely-populated urban areas" , "Large Urban areas" , "Large conurbations" .)