haystack vs stack

haystack and stack both are nouns.

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

As nouns, stack is a hypernym of haystack; that is, stack is a word with a broader meaning than haystack:

haystack (noun)	stack (noun)
a stack of hay	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

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