a.

1. 快的，迅速的；动作快的
   He had a rapid recovery from his illness.

   他迅速恢复了健康。

2. 陡的，险峻的
   The old man had difficulty climbing the rapid ascent.

   这位老人攀登这条陡峭的上坡路有困难。

n.

1. 急流；急湍[P][G]
   The canoeist succeeded in going over the rapids.

   操独木舟者成功地渡过了激流。

2. 城市高速铁路（客车）[C]

adj.

n.