Staff acquiring millions: instant wealth (6)
I believe the answer is:
mammon
'wealth' is the definition.
(mammon is a kind of wealth)
'staff acquiring millions instant' is the wordplay.
'staff' becomes 'man' (manning is a kind of staffing).
'acquiring' indicates putting letters inside.
'millions' becomes 'm' (abbreviation).
'instant' becomes 'mo'.
'm'+'mo'='mmo'
'man' enclosing 'mmo' is 'MAMMON'.
(Other definitions for mammon that I've seen before include "Bible 'You cannot serve God and . . . . . .'" , "Wealth as an object of worship" , "Greed personified" , "money" , "Wealth personified, you cannot serve God an . . . . . ." .)