Plural of cannonball: solid spherical projectiles fired from cannons, or the diving position where you curl into a tight ball.
Compound of 'cannon' (from Italian 'cannone', a large gun) and 'ball' (a sphere). The diving term emerged in the 20th century as pool culture developed.
Cannonballs were terrifyingly simple weapons—just iron spheres—yet they dominated warfare for 400 years; the moment exploding shells were invented, they became obsolete overnight, showing how quickly military technology destroys old advantages.
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