Cannonball/ˈkænənbɔːl/ Definition 1 of 3Pro Tip 1/3Historical Use Cannonballs are from earlier times when cannons were common in battles. Museums display cannonballs from the Civil War era. Pro Tip 2/3Military Context Cannonballs are often mentioned in historical or military discussions. The castle's defenses included a cannon with numerous cannonballs. Pro Tip 3/3Physical Weight Cannonballs are very heavy, symbolizing something with great impact or force. He lifted the heavy box as if it was a cannonball.