Pole has millions invested in bank (6)
I believe the answer is:
camber
'invested in bank' is the definition.
'camber' can be an answer for 'bank' (synonyms). I'm not certain of the 'invested in' bit.
'pole has millions' is the wordplay.
'pole' becomes 'caber' (caber is a kind of pole).
'has' is an insertion indicator.
'millions' becomes 'm' (abbreviation).
'caber' going around 'm' is 'CAMBER'.
Can you help me to learn more?
(Other definitions for camber that I've seen before include "may appear on road" , "Slight tilt" , "Curvature of aircraft wing" , "Upward curve of a road surface" , "Slight upward curve in road, wing etc" .)