red ink vs sum

red ink and sum both are nouns.

Word	Noun	Adjective	Verb	Adverb
red ink	Yes	No	No	No
sum	Yes	No	Yes	No

As nouns, sum is a hypernym of red ink; that is, sum is a word with a broader meaning than red ink:

Other hypernyms of red ink include amount, amount of money, sum of money.

red ink (noun)	sum (noun)
the amount by which the cost of a business exceeds its revenue	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

red ink (verb)	sum (verb)
	determine the sum of
	be a summary of