pile up vs lump

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

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

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

pile up (noun)	lump (noun)
	a compact mass
	a large piece of something without definite shape
	an awkward stupid person
	an abnormal protuberance or localized enlargement

pile up (verb)	lump (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