Poland's capital (6)
I believe the answer is:
warsaw
'poland's capital' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for warsaw that I've seen before include "Capital city on the Vistula" , "Polish capital" , "Largest city in Poland" , "Poland's largest city" , "1929 international agreement regulating commercial air transport" .)