fifth wheel

fifth wheel
noun
(chiefly N. Amer.)(主北美)
  1. an extra wheel for a four-wheeled vehicle
    (四轮车的)备用轮
    ■(informal)a superfluous person or thing
    (非正式)多余的人(或物),累赘
  2. a coupling between a vehicle used for towing and a trailer
    (挂车的)连接轮
    ■(亦作 fifth-wheel trailer)a trailer with accommodation for camping out
    (有生活起居设施的)野营挂车
    ■(historical)a horizontal turntable over the front axle of a carriage as an extra support to prevent its tipping
    (史)〉(马车前车轴上的)转向轮
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