tot up vs sum

tot up is not a noun while sum is a noun.

Word	Noun	Adjective	Verb	Adverb
tot up	No	No	Yes	No
sum	Yes	No	Yes	No

As verbs, tot up and sum are synonyms defined as:

Other synonyms of tot up include add, add together, add up, sum up, summate, tally, tot, total, tote up.

tot up (noun)	sum (noun)
	the whole amount
	the choicest or most essential or most vital part of some idea or experience
	a quantity obtained by the addition of a group of numbers
	the final aggregate
	a set containing all and only the members of two or more given sets
	a quantity of money

tot up (verb)	sum (verb)
determine the sum of	determine the sum of
	be a summary of