Important person with a billion banked? (5)
I believe the answer is:
nabob
'important person' is the definition.
(I've seen this before)
'with a billion banked?' is the wordplay.
'with' is an insertion indicator.
'billion' becomes 'b'.
'banked?' becomes 'nob' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'b'='ab'
'ab' going within 'nob' is 'NABOB'.
(Other definitions for nabob that I've seen before include "Person of great wealth" , "One divining (water)" , "Wealthy and powerful person" , "Wealthy influential person" , "VIP" .)