noun

• (countable) A rejection; a vote against admitting someone.
• (countable) A black ball used to indicate such a negative vote.
  "Regardless how many other people may have voted to approve a candidate for membership, a single blackball will reject the candidate."
• (countable) A kind of large black sweet, a black-colored gobstopper.
• (uncountable) A game, a standardized version of the English version of eight-ball.

verb

• (transitive) To vote against, especially in an exclusive organization.
  "If you're not from a moneyed, well-connected family, you can count on getting blackballed from the fraternity."
• (transitive) To ostracize.
  "Henry knew. If he were blackballed by this distaff Mafia, he was doomed: Endless, but always justifiable, delays would occur in the work he wanted typed."