With diversions, outdo urban one-way system (10)
I believe the answer is:
roundabout
'one-way system' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'with diversions outdo urban' is the wordplay.
'outdo urban' can be anagrammed to 'ROUNDABOUT'.
Though, I'm unsure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for roundabout that I've seen before include "A plaything" , "Traffic controller" , "Roughly" , "devious" , "More or less" .)