Brass component (4)
I believe the answer is:
zinc
'brass component' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for zinc that I've seen before include "Antioxidant element" , "Galvanizing metal" , "Sivery-white metal" , "Metal alloyed with copper to make brass" , "Ingredient in brass" .)