WordNet (r) 3.0 (2006):

cannonball
    n 1: a solid projectile that in former times was fired from a
         cannon [syn: cannonball, cannon ball, round shot]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "cannonball":
   antelope, arrow, ball, bar shot, belly buster, belly flop,
   belly whopper, bird shot, blue darter, blue streak, buckshot,
   bullet, cannon shot, case shot, courser, crash dive, crossbar shot,
   dart, dive, drop, duck shot, dumdum bullet, eagle, electricity,
   expanding bullet, express train, fall, flash, gainer, gazelle,
   grape, grapeshot, greased lightning, greyhound, hare, header,
   jackknife, jet plane, langrel shot, light, lightning,
   manstopping bullet, mercury, nose dive, parachute jump, pellet,
   pitch, plunge, pounce, power dive, quicksilver, rifle ball, rocket,
   round shot, running dive, scared rabbit, shell, shot, shrapnel,
   sky dive, slug, split shot, stationary dive, stoop, streak,
   streak of lightning, striped snake, swallow, swan dive, swoop,
   thought, thunderbolt, torrent, wind