Big city with the old style look (4)
I believe the answer is:
oslo
'big city' is the definition.
'Oslo' can be an answer for 'city' (capital of Norway). I am unsure of the 'big' bit.
'with the old style look' is the wordplay.
'with' is a charade indicator (letters next to each other).
'the old style' becomes 'OS' (used in reference to old-style dates).
'look' becomes 'lo' (archaic exclamation meaning 'look!').
'os' put next to 'lo' is 'OSLO'.
Can you help me to learn more?
(Other definitions for oslo that I've seen before include "Northern capital of Czechoslovakia?" , "foreign port" , "Capital city, called Kristiania until 1924" , "European capital in go-slow" , "European capital city (found in Czechoslovakia!)" .)