subtraction vs step-down

subtraction and step-down both are nouns.

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

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

Other hypernyms of subtraction include decrease, diminution, reduction.

subtraction (noun)	step-down (noun)
the act of subtracting (removing a part from the whole)	the act of decreasing or reducing something
an arithmetic operation in which the difference between two numbers is calculated