noun (n)

• a projectile that is fired from a gun(noun.artifact)

  Synonym:
  slug
  

  source: wordnet30
• a high-speed passenger train(noun.artifact)

  Synonym:
  bullet train
  

  source: wordnet30
• (baseball) a pitch thrown with maximum velocity(noun.act)

  Synonym:
  fastball, heater, hummer, smoke
  

  source: wordnet30
• A small ball.(noun)

  source: webster1913