Be first with a metallic element (4)
I believe the answer is:
lead
This clue is a triple definition!
'be' is the first definition.
(I know that lead is a more specific form of the action be)
'first' is the second definition.
(lead can mean leading or primary)
'with' acts as a link.
'a metallic element' is the third definition.
(I know that lead is a type of metal)
(Other definitions for lead that I've seen before include "Actor playing the principal role" , "Guide the heavy metal" , "Guide, conduct" , "front man" , "shot maybe" .)