Capital of Czechoslovakia (4)
I believe the answer is:
'capital' is the definition.
(capital of Norway)
'of czechoslovakia' is the wordplay.
'of' indicates the answer is hidden within the clue.
'OSLO' can be found hidden inside 'czechoslovakia'.
(Other definitions for oslo that I've seen before include "Norwegian capital" , "Capital in throes of go-slow" , "Location" , "Scandinavian port" , "Northern capital of Czechoslovakia?" .)