A heavy metal; press (4)
I believe the answer is:
iron
I believe this clue is a double definition.
'a heavy metal' is the first definition.
(I've seen this before)
'press' is the second definition.
(I know that press can be written as iron)
(Other definitions for iron that I've seen before include "Metallic element, symbol Fe" , "Press - element" , "Metal (that may be pumped?)" , "Club to smooth the cloth" , "sort of club" .)