Buc·kler n.
 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.
 Note: ☞ 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. Zool. (a) One of the large, bony, external plates found on many ganoid fishes. (b) The anterior segment of the shell of trilobites.
 3. Naut. 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.
 Blind buckler Naut., a solid buckler.
 Buckler mustard Bot., a genus of plants (Biscutella) with small bright yellow flowers. The seed vessel on bursting resembles two bucklers or shields.
 Buckler thorn, a plant with seed vessels shaped like a buckler. See Christ's thorn.
 Riding buckler Naut., a buckler with a hole for the passage of a cable.