Built-up area (4)
I believe the answer is:
town
'built-up area' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for town that I've seen before include "Small urban development" , "Person employed to make public announcements" , "Built up area" , "Milton Keynes, say, with 1a [NEW]" , "Large urban area" .)