bunch up vs clump

bunch up is not a noun while clump is a noun.

Word	Noun	Adjective	Verb	Adverb
bunch up	No	No	Yes	No
clump	Yes	No	Yes	No

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

Other hypernyms of bunch up include cluster, constellate, flock.

bunch up (noun)	clump (noun)
	a heavy dull sound (as made by impact of heavy objects)
	a grouping of a number of similar things
	a compact mass

bunch up (verb)	clump (verb)
form into a bunch	gather or cause to gather into a cluster
	walk clumsily
	come together as in a cluster or flock
	make or move along with a sound as of a horse's hooves striking the ground