Magnate ending in family business, significant amount's banked (6)
I believe the answer is:
tycoon
'magnate' is the definition.
(I know that magnate can be written as tycoon)
'ending in family business significant amount's banked' is the wordplay.
'ending in' says to take the final letters.
'business' becomes 'co' (short for company).
'significant amount' becomes 'ton' (ton can mean a large amount of something).
'banked' means one lot of letters goes inside another (some letters bank or contain others).
The final letter of 'family' is 'y'.
'y'+'co'='yco'
'yco' put inside 'ton' is 'TYCOON'.
(Other definitions for tycoon that I've seen before include "Not coy? (anag)" , "Rich and powerful businessman" , "top businessman" , "Capitalist" , "See 2" .)