domino

Short definition from Wiktionary

Noun

1. 1
   A tile divided into two squares, each having 0 to 6 (or sometimes more) dots or pips (as in dice), used in the game of dominoes.
2. 2
   A country that is expected to react to events in a neighboring country, according to the domino effect.
3. 3
   A masquerade costume consisting of a hooded robe and a mask covering the upper part of the face.
4. 4
   The mask itself.
5. 5
   The person wearing the costume.
6. 6
   A polyomino made up of two squares.
7. 7
   A mistake in performing.
8. 8
   A person's teeth.

Verb

1. 1
   To collapse in the manner of dominoes.
2. 2
   To cause to collapse in the manner of dominoes.