buck vs shoot down

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

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

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

Other synonyms of buck include charge, shoot, tear.

buck (noun)	shoot down (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

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