Mass totals of single payments made at a particular time (4,4)
I believe the answer is:
lump sums
'single payments made at a particular time' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'mass totals' is the wordplay.
'mass' becomes 'lump' (mass can mean a lump or amount of something).
'totals' becomes 'sums' ('sum' can be a synonym of 'total').
'lump'+'sums'='LUMP SUMS'
'of' acts as a link.
Can you help me to learn more?
(Another definition for lump sums that I've seen is " payments".)