- The portion of a hammer containing the metal striking face (also including the claw or peen if so equipped).
- (zoology) An African fruit bat, the hammer-headed fruit bat, Hypsignathus monstrosus, so called from its large blunt nozzle.
- (zoology) A fresh-water fish; the stone-roller, in the minnow family Cyprinidae.
- (biology) A kind of ribozyme; hammerhead ribozyme.
- (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.
- (slang) A stupid person, a dunce.