cannonball

1. A spherical projectile fired from a smoothbore cannon.
2. An explosive-filled hollow iron sphere fused through a hole and intended to explode at a calculated distance rather than explode on impact.
3. 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. · The New Yorker, 30 August 2004, p.40· The cannonball could be called the S.U.V. of the pool — oversized, brash, hormonally hardwired.
4. Something that moves fast, especially a fast train. (figuratively, slang) · Meetings of the model train club always begin with the song "Wabash Cannonball".
5. A served ball that travels with great speed and describes little or no arc in flight.

Plural cannonballs