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

in sum

: as a brief statement of the most important information in a piece of writing or speech
: 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.
see also zero-sum game
2 sum /ˈsʌm/ verb
sums; summed; summing
2 sum
sums; summed; summing
Learner's definition of SUM

sum up

[phrasal verb]
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
sum up (someone or something) or sum (someone or something) up
: to describe or show the most important parts or qualities of (someone or something) in a brief or simple way
: to describe (someone or something) using few words
see also summing-up