pile up vs gather

pile up is not a noun while gather is a noun.

Word	Noun	Adjective	Verb	Adverb
pile up	No	No	Yes	No
gather	Yes	No	Yes	No

As verbs, pile up and gather are synonyms defined as:

Other synonyms of pile up include accumulate, amass, conglomerate, cumulate.

As verbs, gather is a hypernym of pile up; that is, gather is a word with a broader meaning than pile up:

Other hypernyms of pile up include collect, garner, pull together.

pile up (noun)	gather (noun)
	the act of gathering something
	sewing consisting of small folds or puckers made by pulling tight a thread in a line of stitching

pile up (verb)	gather (verb)
increase in amount by collecting or gathering	increase in amount by collecting or gathering
arrange into piles or stacks	increase or develop
get or gather together	conclude from evidence
	assemble or get together
	draw together into folds or puckers
	look for (food) in nature
	draw and bring closer
	collect in one place
	get people together