step on it vs buck

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

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

As verbs, buck is a hyponym of step on it; that is, buck is a word with a more specific, narrower meaning than step on it:

Other hyponyms of step on it include barge, push forward, thrust ahead, charge, shoot, shoot down, tear, dart, dash, flash, scoot, scud, shoot.

step on it (noun)	buck (noun)
	mature male of various mammals (especially deer or antelope)
	a framework for holding wood that is being sawed
	a gymnastic horse without pommels and with one end elongated; used lengthwise for vaulting
	a piece of paper money worth one dollar

step on it (verb)	buck (verb)
move hurridly	jump vertically, with legs stiff and back arched
	move quickly and violently
	resist
	to strive with determination