The capital of South Dakota (6)
I believe the answer is:
pierre
'the capital of south dakota' is the definition.
('Pierre' can be a synonym of 'capital of south dakota')
This is all the clue.
(Other definitions for pierre that I've seen before include "One colouring cloth" , "See 17" , "Frenchman" , "Peter in France" , "French boy's name" .)