shoot down vs veto

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

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

As verbs, veto is a hypernym of shoot down; that is, veto is a word with a broader meaning than shoot down:

Other hypernyms of shoot down include blackball, negative.

shoot down (noun)	veto (noun)
	a vote that blocks a decision
	the power or right to prohibit or reject a proposed or intended act (especially the power of a chief executive to reject a bill passed by the legislature)

shoot down (verb)	veto (verb)
shoot at and force to come down	command against
move quickly and violently	vote against; refuse to endorse; refuse to assent
thwart the passage of