0 a ball used in the game of billiards (= a game played by two people on a table covered in soft cloth, in which a long stick is used to hit balls against each other and into pockets around the table): --
Now you can see in the picture that I am bald as a billiard ball.
Like billiard balls scattered on a pool table, the stories collide and coexist.
His best-known discovery, made in the search of a substitute for the ivory used in billiard balls, was the plastic celluloid.
When you do physics, you study rather boring sorts of objects, like billiard balls that collide and so on.