round up vs gather

round up is not a noun while gather is a noun.

Word	Noun	Adjective	Verb	Adverb
round up	No	No	Yes	No
gather	Yes	No	Yes	No

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

Other hypernyms of round up include collect, garner, pull together.

round up (noun)	gather (noun)
	the act of gathering something
	sewing consisting of small folds or puckers made by pulling tight a thread in a line of stitching

round up (verb)	gather (verb)
seek out and bring together	increase in amount by collecting or gathering
	increase or develop
	conclude from evidence
	assemble or get together
	draw together into folds or puckers
	look for (food) in nature
	draw and bring closer
	collect in one place
	get people together