/kan"euhn bawl'/ , n. Also, cannon ball .
1. a missile, usually round and made of iron or steel, designed to be fired from a cannon.
2. Tennis. a served ball that travels with great speed and describes little or no arc in flight.
3. anything that moves with great speed, as an express train.
adj.
4. made from a curled-up position with the arms pressing the knees against one's chest: a cannonball dive.
5. moving at great speed: a train known as a cannonball express.
[ 1655-65; CANNON + BALL 1 ]