Silver coin and money supply in kingdom (5)
I believe the answer is:
realm
'kingdom' is the definition.
(thesaurus)
'silver coin and money supply' is the wordplay.
'silver coin' becomes 'real' (Spanish real**).
'and' means one lot of letters go next to another.
'money supply' becomes 'm' (economics abbreviation).
'real'+'m'='REALM'
'in' is the link.
(Other definitions for realm that I've seen before include "Kingdom could be lamer" , "King's domain" , "Land under a king or queen" , "Kingdom; field of interest" , "monarch's responsibility" .)