blackball vs vote down

blackball is a noun but vote down is not a noun.

Word	Noun	Adjective	Verb	Adverb
blackball	Yes	No	Yes	No
vote down	No	No	Yes	No

As verbs, vote down is a hyponym of blackball; that is, vote down is a word with a more specific, narrower meaning than blackball:

Other hyponyms of blackball include defeat, kill, shoot down, vote out.

blackball (noun)	vote down (noun)
the act of excluding someone by a negative vote or veto

blackball (verb)	vote down (verb)
expel from a community or group	thwart the passage of
vote against; refuse to endorse; refuse to assent	vote against