Powder used in capital city (4)
I believe the answer is:
talc
'powder' is the definition.
(talcing is a kind of powdering)
'in capital city' is the wordplay.
'in' says the answer is hidden in the clue.
'TALC' is hidden within 'capital city'.
'used' is the link.
(Other definitions for talc that I've seen before include "Baby powder" , "Mineral used as a toiletry" , "Bathroom dusting powder" , "Softest mineral on Mohs hardness scale" , "Powdered mineral" .)