Buckler

Noun

 * 1) A kind of shield, of various shapes and sizes, worn on one of the arms (usually the left) for protecting the front of the body.  In the sword and buckler play of the Middle Ages in England, the buckler was a small shield, used, not to cover the body, but to stop or parry blows.
 * 2)  A shield resembling the Roman scutum. In modern usage, a smaller variety of shield is usually implied by this term.
 * 3)  One of the large, bony, external plates found on many ganoid fishes.
 * 4)  The anterior segment of the shell of trilobites.
 * 5)  A block of wood or plate of iron made to fit a hawse hole, or the circular opening in a half-port, to prevent water from entering when the vessel pitches.