sum

1 sum /ˈsʌm/ noun
plural sums
1 sum
/ˈsʌm/
noun
plural sums
Britannica Dictionary definition of SUM
1 
[count] : an amount of money
— see also lump sum
2 
[count]
a  : the result of adding two or more numbers together
b  : a simple problem in mathematics — usually plural
3 
[singular] : the whole amount of something
— see also sum total

in sum

1 
: as a brief statement of the most important information in a piece of writing or speech
2 
: in a few words

sum and substance

: the general or basic meaning of something said or written

sum of its parts

◊ Something that is greater/better/more than the sum of its parts is better or more effective as a team, combination, etc., than you would expect it to be when you look at the different parts that form it.
2 sum /ˈsʌm/ verb
sums; summed; summing
2 sum
/ˈsʌm/
verb
sums; summed; summing
Britannica Dictionary definition of SUM

sum up

[phrasal verb]
1 
sum up or sum up (something) or sum (something) up : to tell (information) again using fewer words : to give a summary of (statements, facts, etc.) : summarize
2 
sum up (someone or something) or sum (someone or something) up
a  : to describe or show the most important parts or qualities of (someone or something) in a brief or simple way
b  : to describe (someone or something) using few words
— see also summing-up