Reportedly a remarkable amount of money (3)
I believe the answer is:
sum
'amount of money' is the definition.
(synonyms)
'reportedly a remarkable' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'a remarkable' becomes 'some' (that's some car you've got!).
'some' sounds like 'SUM'.
(Other definitions for sum that I've seen before include "An additional problem" , "Quantity of money" , "See 25" , "pupils find it a problem" , "Amount, aggregate" .)