bunch together vs flock

bunch together is not a noun while flock is a noun.

Word	Noun	Adjective	Verb	Adverb
bunch together	No	No	Yes	No
flock	Yes	No	Yes	No

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

Other hypernyms of bunch together include clump, cluster, constellate.

bunch together (noun)	flock (noun)
	a group of birds
	a group of sheep or goats
	a church congregation guided by a pastor
	an orderly crowd
	(often followed by `of') a large number or amount or extent

bunch together (verb)	flock (verb)
form into a bunch	come together as in a cluster or flock
	move as a crowd or in a group