Magnificent sum of money (5)
I believe the answer is:
grand
I believe this clue is a double definition.
'magnificent' is the first definition.
(I've seen this in another clue)
'sum of money' is the second definition.
(a thousand pounds)
(Other definitions for grand that I've seen before include "Comprehensive" , "Fine" , "GBP1,000" , "great distinction" , "Magnificent, imposing" .)