Nine to five he goes round the old city (7)
I believe the answer is:
nineveh
'the old city' is the definition.
(ancient Assyrian city)
'nine to five he goes round' is the wordplay.
'to five' becomes 'V' (Roman numeral).
'goes round' shows that the letters should be reversed in order.
'he' back-to-front is 'eh'.
'nine'+'v'+'eh'='NINEVEH'
(Other definitions for nineveh that I've seen before include "Ancient Assyrian capital" , "Ancient city on the Tigris" , "old city" , "Assyrian capital; Jonah preached against it" , "Ancient Assyrian city" .)