Street silver speculator (4)
I believe the answer is:
stag
'speculator' is the definition.
(thesaurus)
'street silver' is the wordplay.
'street' becomes 'st'.
'silver' becomes 'ag' (Ag is the chemical symbol for silver).
'st'+'ag'='STAG'
(Other definitions for stag that I've seen before include "in a rut, perhaps?" , "Male beast" , "Male animal" , "Stock market speculator" , "One who speculates" .)