A chap with millions in capital (5)
I believe the answer is:
amman
'capital' is the definition.
(capital of Jordan)
'a chap with millions' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'with' is an insertion indicator.
'millions' becomes 'm' (abbreviation).
'man' enclosing 'm' is 'mman'.
'a'+'mman'='AMMAN'
'in' is the link.
(Other definitions for amman that I've seen before include "A capital f-fellow in Jordan?" , "Jordanian city" , "Jordanian capital" , "Jordan's capital" , "City of Jordan" .)