split down vs step-down

split down and step-down both are nouns.

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

As nouns, step-down is a hypernym of split down; that is, step-down is a word with a broader meaning than split down:

split down: a decrease in the number of outstanding shares of a corporation without changing the shareholders' equity
step-down: the act of decreasing or reducing something

Other hypernyms of split down include decrease, diminution, reduction.

split down (noun)	step-down (noun)
a decrease in the number of outstanding shares of a corporation without changing the shareholders' equity	the act of decreasing or reducing something