pile up vs chunk

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

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

As verbs, chunk is a hyponym of pile up; that is, chunk 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, scratch, lump, bale, catch, fund, fund.

pile up (noun)	chunk (noun)
	a compact mass
	a substantial amount

pile up (verb)	chunk (verb)
increase in amount by collecting or gathering	group or chunk together in a certain order or place side by side
arrange into piles or stacks	put together indiscriminately
get or gather together