stack up vs stack

stack up is not a noun while stack is a noun.

Word	Noun	Adjective	Verb	Adverb
stack up	No	No	Yes	No
stack	Yes	No	Yes	No

stack up (noun)	stack (noun)
	a large tall chimney through which combustion gases and smoke can be evacuated
	a storage device that handles data so that the next item to be retrieved is the item most recently stored (LIFO)
	a list in which the next item to be removed is the item most recently stored (LIFO)
	an orderly pile
	(often followed by `of') a large number or amount or extent

stack up (verb)	stack (verb)
arrange into piles or stacks	arrange in stacks
	load or cover with stacks
	arrange the order of so as to increase one's winning chances