lump vs pile up

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

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

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

Other hypernyms of lump include accumulate, amass, collect, compile, hoard, roll up.

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

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