Anvil metal (4)
I believe the answer is:
iron
'anvil metal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iron that I've seen before include "The metallic element plays a role in the transport of oxygen by the blood" , "Smooth - press - club" , "Heavy metal that rusts easily" , "Main element in steel" , "The one who was 'not for turning'" .)