What does "buckler" mean?

Buckler: (Zoöl.) (a) One of the large, bony, external plates found on many ganoid fishes. (b) The anterior segment of the shell of trilobites.

Additional senses

  1. 2.(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.
  2. 3.To shield; to defend. [Obs.] Can Oxford, that did ever fence the right, Now buckler falsehood with a pedigree Shak.

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