sum vs summate

sum is a noun but summate is not a noun.

Word	Noun	Adjective	Verb	Adverb
sum	Yes	No	Yes	No
summate	No	No	Yes	No

As verbs, sum and summate are synonyms defined as:

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

sum (noun)	summate (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

sum (verb)	summate (verb)
determine the sum of	determine the sum of
be a summary of	form or constitute a cumulative effect