WordNet
n. ball used in playing billiards
Wikipedia
A billiard ball is a small, hard ball used in cue sports, such as carom billiards, pool, and snooker. The number, type, diameter, color, and pattern of the balls differ depending upon the specific game being played. Various particular ball properties such as hardness, friction coefficient and resilience are important to accuracy.
Usage examples of "billiard ball".
But imagine how much friction it would take to slow up an object the mass of a billiard ball going at the speed of light.
She hit the target, and there was an audible thud as the billiard ball connected with Elton's skull, causing him to roar in pain.
And then-I was watching it as it happened-a second billiard ball popped out of one of the table's pockets, quite spontaneously, and began to roll, square on, towards my ball at rest at the centre of the table.