shoot down vs buck

shoot down is not a noun while buck is a noun.

Word	Noun	Adjective	Verb	Adverb
shoot down	No	No	Yes	No
buck	Yes	No	Yes	No

As verbs, shoot down and buck are synonyms defined as:

Other synonyms of shoot down include charge, shoot, tear.

shoot down (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

shoot down (verb)	buck (verb)
shoot at and force to come down	jump vertically, with legs stiff and back arched
move quickly and violently	move quickly and violently
thwart the passage of	resist
	to strive with determination