Etymology
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blackball (v.)

also black-ball, "to exclude from a club by adverse votes," 1770, from black (adj.) + ball (n.1). The image is of the black balls of wood or ivory that were dropped into an urn as adverse votes during secret ballots. Related: Blackballed; blackballing.

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Definitions of blackball
1
blackball (v.)
expel from a community or group;
Synonyms: banish / ban / ostracize / ostracise / shun / cast out
blackball (v.)
vote against; refuse to endorse; refuse to assent;
Synonyms: veto / negative
2
blackball (n.)
the act of excluding someone by a negative vote or veto;
Synonyms: barring
From wordnet.princeton.edu