fall down 倒下，倒塌，失败

最基本的含义为掉在地上，或者从上至下掉落下来，fall down a cliff 表示从悬崖上掉下来， fall down the stairs 表示在从台阶上摔下来。也可以用来表示“失败”。

例句：

My father fell down the stairs the other day.

我爸爸有一天从楼梯上摔了下来。

I fell down the stairs and broke my tooth.

我从楼梯上摔了下来，摔掉了牙。

The building fell down. Three people were crushed to death.

那座建筑倒塌了，3 个人被压死了。

对话：

A: There is a lot of ice on the sidewalks today.

今天人行道上结了很厚的冰。

B: Be careful that you don't fall down.

小心点，别摔倒了。