US city showing elegance in the past (7)
I believe the answer is:
chicago
'us city' is the definition.
(I've seen this before)
'elegance in the past' is the wordplay.
'elegance' becomes 'chic' (chic is a kind of elegance).
'in the past' becomes 'ago' ('ago' can be a synonym of 'in the past').
'chic'+'ago'='CHICAGO'
'showing' is the link.
(Other definitions for chicago that I've seen before include "A Windy City in Illinois" , "Windy City of USA" , "US city - musical featuring All That Jazz" , "A windy place" , "Musical (in Illinois?)" .)