Object over note describing this US city (5)
I believe the answer is:
miami
'this us city' is the definition.
(I've seen this before)
'object over note' is the wordplay.
'object' becomes 'aim' (synonyms).
'over' is a reversal indicator.
'note' becomes 'mi' (musical note).
'aim' backwards is 'mia'.
'mia'+'mi'='MIAMI'
'describing' is the link.
(Other definitions for miami that I've seen before include "Port in Florida" , "Popular city in SE Florida" , "tourist centre" , "Floridian city" , "US city" .)