Metal conductor (4)
I believe the answer is:
lead
I believe this clue is a double definition.
'metal' is the first definition.
(I know that lead is a type of metal)
'conductor' is the second definition.
(I know that lead is a type of conducting wire)
(Other definitions for lead that I've seen before include "Metal; show the way" , "Sort of poisoning" , "Principal role in a play" , "Metal - van - go ahead" , "Guide,direct" .)