Heavy metal at 1 (4)
I believe the answer is:
lead
This clue could be a double definition.
'heavy' is the first definition.
(thesaurus)
'metal at 1' is the second definition.
'lead' can be an answer for 'metal' (I've seen this in another clue). I am not sure about the 'at 1' bit.
Can you help me to learn more?
(Other definitions for lead that I've seen before include "Heavy malleable metallic element" , "1 down, symbol Pb" , "Top actor" , "Guide the heavy metal" , "Call the shots" .)