The man goes round a square in Rome where it's busy (4)
I believe the answer is:
hive
'where it's busy' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'the man goes round a square in rome' is the wordplay.
'the man' becomes 'he' (he refers to a man).
'goes round' indicates putting letters inside.
'a square in rome' becomes 'iv' (I can't justify this - if you can you should believe this answer much more).
'he' going around 'iv' is 'HIVE'.
Can you help me to learn more?
(Other definitions for hive that I've seen before include "Apiary abode" , "Home for bees" , "busy scene" , "home of queen" , "Scene of activity" .)