step-down vs decrease

step-down and decrease both are nouns.

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

As nouns, step-down and decrease are synonyms defined as:

Other synonyms of step-down include diminution, reduction.

step-down (noun)	decrease (noun)
the act of decreasing or reducing something	the act of decreasing or reducing something
	the amount by which something decreases
	a change downward
	a process of becoming smaller or shorter

step-down (verb)	decrease (verb)
	decrease in size, extent, or range
	make become smaller