number vs sum

number and sum both are nouns.

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

As verbs, sum is a hyponym of number; that is, sum is a word with a more specific, narrower meaning than number:

Other hyponyms of number include recount, miscount, census, add, add together, add up, sum up, summate, tally, tot, tot up, total, tote up.

number (noun)	sum (noun)
an item of clothing	the whole amount
the property possessed by a sum or total or indefinite quantity of units or individuals	the choicest or most essential or most vital part of some idea or experience
a clothing measurement	a quantity obtained by the addition of a group of numbers
one of a series published periodically	the final aggregate
a symbol used to represent a number	a set containing all and only the members of two or more given sets
a numeral or string of numerals that is used for identification and may be attached to accounts, memberships, etc.	a quantity of money
the number is used in calling a particular telephone
a short performance that is part of a longer program
the grammatical category for the forms of nouns and pronouns and verbs that are used depending on the number of entities involved (singular or dual or plural)
a numbered item in a series
a select company of people
a concept of quantity involving zero and units

number (verb)	sum (verb)
place a limit on the number of	determine the sum of
determine the number or amount of	be a summary of
enumerate
give numbers to
add up in number or quantity
put into a group