forgather vs clump

forgather is not a noun while clump is a noun.

Word	Noun	Adjective	Verb	Adverb
forgather	No	No	Yes	No
clump	Yes	No	Yes	No

As verbs, clump is a hyponym of forgather; that is, clump is a word with a more specific, narrower meaning than forgather:

forgather (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

forgather (verb)	clump (verb)
collect in one place	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