Southern Greek character raised total (3)
I believe the answer is:
sum
'total' is the definition.
(I know that total can be written as sum)
'southern greek character raised' is the wordplay.
'southern' becomes 's' (abbreviation).
'greek character' becomes 'mu' (letter from the Greek alphabet).
'raised' shows that the letters should be reversed in order (going up in a down clue).
'mu' in reverse letter order is 'um'.
's'+'um'='SUM'
(Other definitions for sum that I've seen before include "Arithmetical problem" , "Arithmetic calculation" , "Amount, of money say" , "Total, add" , "Aggregate, total" .)