City of Czechoslovakia (4)
I believe the answer is:
oslo
'city' is the definition.
(Norwegian city)
'of czechoslovakia' is the wordplay.
'of' indicates a hidden word.
'OSLO' can be found hidden inside 'czechoslovakia'.
(Other definitions for oslo that I've seen before include "Northern city" , "Capital often frozen" , "Location" , "European capital, known until 1924 as Christiania" , "Norway's capital city" .)