Capital of Slovenia, Ljubljana obvious initially (4)
I believe the answer is:
oslo
'capital' is the definition.
(Oslo is an example)
'of slovenia ljubljana obvious initially' is the wordplay.
'initially' says to take the initial letters.
The initial letters of 'of slovenia ljubljana obvious' is 'OSLO'.
(Other definitions for oslo that I've seen before include "Capital city, called Kristiania until 1924" , "European capital city (found in Czechoslovakia!)" , "It's capital in Anglos London" , "Northern capital of Czechoslovakia?" , "Nordic city" .)