pile up vs scratch

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

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

As verbs, scratch is a hyponym of pile up; that is, scratch is a word with a more specific, narrower meaning than pile up:

Other hyponyms of pile up include run up, corral, collect, pull in, come up, scrape, scrape up, chunk, lump, bale, catch, fund, fund.

pile up (noun)	scratch (noun)
	an indication of damage
	(golf) a handicap of zero strokes
	poor handwriting
	a harsh noise made by scraping
	dry mash for poultry
	a line indicating the location of the start of a race or a game
	a competitor who has withdrawn from competition
	informal terms for money
	a depression scratched or carved into a surface
	an abraded area where the skin is torn or worn off

pile up (verb)	scratch (verb)
increase in amount by collecting or gathering	cut the surface of; wear away the surface of
arrange into piles or stacks	cause friction
get or gather together	carve, cut, or etch into a material or surface
	gather (money or other resources) together over time
	remove by erasing or crossing out or as if by drawing a line
	scrape or rub as if to relieve itching
	postpone indefinitely or annul something that was scheduled