shoot down vs shoot

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

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

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

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

shoot down (noun)	shoot (noun)
	the act of shooting at targets
	a new branch

shoot down (verb)	shoot (verb)
shoot at and force to come down	give an injection to
move quickly and violently	produce buds, branches, or germinate
thwart the passage of	measure the altitude of by using a sextant
	record on photographic film
	make a film or photograph of something
	utter fast and forcefully
	fire a shot; release
	hit with a missile from a weapon
	score
	spend frivolously and unwisely
	force or drive (a fluid or gas) into by piercing
	throw or propel in a specific direction or towards a specific objective
	throw dice, as in a crap game
	variegate by interweaving weft threads of different colors
	run or move very quickly or hastily
	move quickly and violently
	send forth suddenly, intensely, swiftly
	cause a sharp and sudden pain in
	kill by firing a missile
	emit (as light, flame, or fumes) suddenly and forcefully