Silver coin added to millions in kingdom (5)
I believe the answer is:
realm
'kingdom' is the definition.
(I've seen this before)
'silver coin added to millions' is the wordplay.
'silver coin' becomes 'real' (Spanish real).
'added to' says to put letters next to each other.
'millions' becomes 'm' (abbreviation).
'real'+'m'='REALM'
'in' acts as a link.
(Other definitions for realm that I've seen before include "Kingdom, domain" , "Kingdom, or field of activity" , "Royal domain" , "region" , "Area of influence" .)