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