Trade in lead forms (4)
I believe the answer is:
deal
'trade in' is the definition.
'lead forms' is the wordplay.
'forms' is an anagram indicator.
'lead' anagrammed gives 'DEAL'.
(Other definitions for deal that I've seen before include "Loss of life" , "Act of business" , "Treat" , "Soft wood; trade" , "understanding" .)