Falsify, counterfeit (5)
I believe the answer is:
forge
I believe this clue is a double definition.
'falsify' is the first definition.
(thesaurus)
'counterfeit' is the second definition.
(synonyms)
(Other definitions for forge that I've seen before include "Shape by heating and hammering, as smith does" , "Smith's workplace" , "Smithy; falsify" , "Smith's workshop" , "Create; counterfeit" .)