hammerhead

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The head of a hammer.
2. n. Any of several predatory sharks of the genus Sphyrna, having the sides of the head elongated into fleshy extensions with the eyes at the ends.
3. n. A wading bird (Scopus umbretta) of Africa and southwest Asia, having brown plumage, a large bladelike bill, and a long backward-pointing crest. Also called hammerkop, umbrette.
4. n. An African fruit bat (Hypsignathus monstrosus), the male of which has a distinctive enlarged head.

Century Dictionary and Cyclopedia

1. n. A shark of the family Sphyrnidæ or Zygœnidæ: so called from the great lateral expansion of the head. There are 3 genera and 5 species, inhabiting most seas. The common species is Sphyrna zygœna, better known as Zygœna malleus, a cosmopolitan species which attains a length of from 12 to 15 feet. Those with the head less hammer-like belong to the genus Reniceps, and are commonly called shovelheads.
2. n. A catostomine fish, Hypentelium nigricans, having a peculiarly shaped head, which is flat above and transversely concave between the eyes, while the snout is abruptly turned down. It abounds in the fresh waters of the United States, from New York to Kansas and Alabama. It sometimes attains a length of two feet. Other names are hogsucker, stone-roller, and crawl-a-bottom.
3. n. The umber or shadow-bird, Scopus umbretta.
4. n. In pianoforte-making, the padded projection of the hammer which strikes against the string.

Wiktionary

1. n. The portion of a hammer containing the metal striking face (also including the claw or peen if so equipped).
2. n. zoology Any of various sharks of the genus Sphyrna or Zygaena having the eyes set on projections from the sides of the head, which gives it a hammer shape.
3. n. zoology A fresh-water fish; the stone-roller, in the minnow family Cyprinidae.
4. n. zoology An African fruit bat, the hammer-headed fruit bat, Hypsignathus monstrosus, so called from its large blunt nozzle.
5. n. slang A stupid person, a dunce.
6. n. biology A kind of ribozyme; Hammerhead ribozyme.

GNU Webster's 1913

1. n. (Zoöl.) 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.
2. n. (Zoöl.) A fresh-water fish; the stone-roller.
3. n. (Zoöl.) An African fruit bat (Hypsignathus monstrosus); -- so called from its large blunt nozzle.

WordNet 3.0

1. n. medium-sized live-bearing shark with eyes at either end of a flattened hammer-shaped head; worldwide in warm waters; can be dangerous
2. n. a stupid person; these words are used to express a low opinion of someone's intelligence
3. n. the striking part of a hammer