Meaning

• A rejection; a vote against admitting someone.

• 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."

• A kind of large black sweet; a niggerball.

• A substance for blacking shoes, boots, etc. or for taking impressions of engraved work.

Meaning

• 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."

• To ostracize.