noun (n)

• a singer who produces a tune without opening the lips or forming words(noun.person)

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

  Synonym:
  bullet, fastball, heater, smoke
  

  source: wordnet30
• One who, or that which, hums; one who applauds by humming.(noun)

  source: webster1913