cannonball

A spherical projectile fired from a smoothbore cannon.

An explosive-filled hollow iron sphere fused through a hole and intended to explode at a calculated distance rather than explode on impact.

(diving) The act of jumping (typically into a swimming pool) with the legs bent and the arms wrapped around the knees to create a large splash, mimicking the flight and shape of a cannonball.

(slang, figuratively) Something that moves fast, especially a fast train.

(tennis) A served ball that travels with great speed and describes little or no arc in flight.