buck·board /-ˌbord, ˌbɔrd/
  四輪馬車的一種
  Buck·board n. A four-wheeled vehicle, having a long elastic board or frame resting on the bolsters or axletrees, and a seat or seats placed transversely upon it; -- called also buck wagon.
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  buckboard
       n : an open horse-drawn carriage with four wheels; has a seat
           attached to a flexible board between the two axles