step-up vs split up

step-up and split up both are nouns.

Word	Noun	Adjective	Verb	Adverb
step-up	Yes	No	No	No
split up	Yes	No	Yes	No

As nouns, split up is a hyponym of step-up; that is, split up is a word with a more specific, narrower meaning than step-up:

step-up: the act of increasing something
split up: an increase in the number of outstanding shares of a corporation without changing the shareholders' equity

step-up (noun)	split up (noun)
the act of increasing something	an increase in the number of outstanding shares of a corporation without changing the shareholders' equity

step-up (verb)	split up (verb)
	become separated into pieces or fragments
	get a divorce; formally terminate a marriage
	discontinue an association or relation; go different ways
	separate into parts or portions