1. To become black
2. To make black
3. To declare (as a business or industry) subject to boycott by trade-union members (chiefly British)
4. Blackball, vote against, especially by placing a black ball in the ballot box; reject for membership; exile.

To make or become black; SYN. melanize, nigrify, black.

A substance (as a paste or polish) that is applied to an object to make it black.