noun (n)

• a stupid person; these words are used to express a low opinion of someone's intelligence(noun.person)

  Synonym:
  blockhead, bonehead, dumbass, dunce, dunderhead, fuckhead, knucklehead, loggerhead, lunkhead, muttonhead, numskull, shithead
  

  source: wordnet30
• the striking part of a hammer(noun.artifact)

  source: wordnet30
• medium-sized live-bearing shark with eyes at either end of a flattened hammer-shaped head; worldwide in warm waters; can be dangerous(noun.animal)

  Synonym:
  hammerhead shark
  

  source: wordnet30
• A shark of the genus Sphyrna or Zygæna, having the eyes set on projections from the sides of the head, which gives it a hammer shape. The Sphyrna zygæna is found in the North Atlantic. Called also hammer fish, and balance fish.(noun)

  source: webster1913