Copper put in malt mixed with powder (6)
I believe the answer is:
talcum
'powder' is the definition.
(talcum is a kind of powder)
'copper put in malt mixed' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'put in' is an insertion indicator.
'mixed' indicates anagramming the letters.
'malt' with letters rearranged gives 'talm'.
'cu' inserted inside 'talm' is 'TALCUM'.
'with' acts as a link.
(Other definitions for talcum that I've seen before include "Dusting powder" , "Scented toilet powder" , "Powder used on the body" , "Bathroom mineral" , "Type of powder" .)