unitize vs split up

unitize is not a noun while split up is a noun.

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

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

Other hypernyms of unitize include carve up, dissever, divide, separate, split.

unitize (noun)	split up (noun)
	an increase in the number of outstanding shares of a corporation without changing the shareholders' equity

unitize (verb)	split up (verb)
separate or classify into units	become separated into pieces or fragments
make into a unit	get a divorce; formally terminate a marriage
divide (bulk material) and process as units	discontinue an association or relation; go different ways
	separate into parts or portions