boulder /ˈbəʊldə/ star1 (boulders)

• 1.  

  N-COUNT（可数名词） A boulder is a large rounded rock. 圆形巨石

  例：

  It is thought that the train hit a boulder that had fallen down a cliff on to the track.

  人们认为这列火车撞到了从悬崖滚到铁轨上的大圆石。