<p><strong>Noun</strong></p><ul><li>a missile, usually round and made of iron or steel, designed to be fired from a cannon.</li><li>Tennis: a served ball that travels with great speed and describes little or no arc in flight.</li><li>anything that moves with great speed, as an express train.</li></ul><p><strong>Adjective</strong></p><ul><li>made from a curled-up position with the arms pressing the knees against one's chest: a cannonball dive.</li><li>moving at great speed: a train known as a cannonball express.</li></ul>