split vs break up

split is a noun but break up is not a noun.

Word	Noun	Adjective	Verb	Adverb
split	Yes	Yes	Yes	No
break up	No	No	Yes	No

As verbs, break up is a hyponym of split; that is, break up is a word with a more specific, narrower meaning than split:

Other hyponyms of split include disperse, dissipate, scatter, spread out, diffract.

As verbs, split and break up are synonyms defined as:

split and break up: discontinue an association or relation; go different ways

Other synonyms of split include break, part, separate, split up.

split (noun)	break up (noun)
division of a group into opposing factions
the act of rending or ripping or splitting something
extending the legs at right angles to the trunk (one in front and the other in back)
an increase in the number of outstanding shares of a corporation without changing the shareholders' equity
(tenpin bowling) a divided formation of pins left standing after the first bowl
a dessert of sliced fruit and ice cream covered with whipped cream and cherries and nuts
an opening made forcibly as by pulling apart
a lengthwise crack in wood
a promised or claimed share of loot or money
a bottle containing half the usual amount

split (adjective)	break up (adjective)
(especially of wood) cut or ripped longitudinally with the grain
having been divided; having the unity destroyed

split (verb)	break up (verb)
come open suddenly and violently, as if from internal pressure	laugh unrestrainedly
separate or cut with a tool, such as a sharp instrument	break or cause to break into pieces
go one's own way; move apart	come to an end
discontinue an association or relation; go different ways	separate (substances) into constituent elements or parts
separate into parts or portions	cause to go into a solution
	cause to separate
	close at the end of a session
	bring the association of to an end or cause to break up
	make a break in
	set or keep apart
	break violently or noisily; smash
	attack with or as if with a pickaxe of ice or rocky ground, for example
	release ice
	destroy the completeness of a set of related items
	take apart into its constituent pieces
	suffer a nervous breakdown
	disband
	to cause to separate and go in different directions
	discontinue an association or relation; go different ways