1.  hammerhead(n = noun.person) blockhead, bonehead, dumbass, dunce, dunderhead, fuckhead, knucklehead, loggerhead, lunkhead, muttonhead, numskull, shithead - a stupid person; these words are used to express a low opinion of someone's intelligence;
is a kind of dolt, dullard, pillock, poor fish, pudden-head, pudding head, stupe, stupid, stupid person

2.  hammerhead(n = noun.artifact) - the striking part of a hammer;
is a kind of head
is a part of hammer
has parts: peen

3.  hammerhead(n = noun.animal) hammerhead shark - medium-sized live-bearing shark with eyes at either end of a flattened hammer-shaped head; worldwide in warm waters; can be dangerous;
is a kind of shark
is a member of genus sphyrna, sphyrna
has particulars: smooth hammerhead, sphyrna zygaena, smalleye hammerhead, sphyrna tudes, bonnet shark, bonnethead, shovelhead, sphyrna tiburo

1.  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. [1913 Webster]

2.  A fresh-water fish; the stone-roller. [1913 Webster]

3.  An African fruit bat (Hypsignathus monstrosus); -- so called from its large blunt nozzle. [1913 Webster]

hammerhead, n.
1 any shark of the family Sphyrinidae, with a flattened head and eyes in lateral extensions of it.
2 a long-legged African marsh-bird, Scopus umbretta, with a thick bill and an occipital crest.

hammerhead shark, smalleye hammerhead, smooth hammerhead