Completely ruin sum (5)
I believe the answer is:
total
This clue could be a double definition.
'completely ruin' is the first definition.
'total' can be an answer for 'ruin' (total can mean to totally ruin something). I am unsure of the 'completely' bit.
'sum' is the second definition.
(I know that sum can be written as total)
Can you help me to learn more?
(Other definitions for total that I've seen before include "Utter" , "Everything added together" , "The whole number" , "Sum, aggregation" , "Including all" .)