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
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