step on it vs speed

step on it is not a noun while speed is a noun.

Word	Noun	Adjective	Verb	Adverb
step on it	No	No	Yes	No
speed	Yes	No	Yes	No

As verbs, step on it and speed are synonyms defined as:

Other synonyms of step on it include belt along, bucket along, cannonball along, hasten, hie, hotfoot, pelt along, race, rush, rush along.

step on it (noun)	speed (noun)
	changing location rapidly
	a central nervous system stimulant that increases energy and decreases appetite; used to treat narcolepsy and some forms of depression
	a rate (usually rapid) at which something happens
	the ratio of the focal length to the diameter of a (camera) lens system
	distance travelled per unit time

step on it (verb)	speed (verb)
move hurridly	move faster
	cause to move faster
	move very fast
	travel at an excessive or illegal velocity
	move hurridly