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.-one of the large, bony, external plates found on many ganoid fishes.-the anterior segment of the shell of trilobites.-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.-to shield; to defend.