河马用英语叫做 hippopotamus。该词来源于希腊语，hippos 意为马，potamos 意为河流。例句如下：

The hippopotamus is a large, semi-aquatic mammal. 河马是一种大型的半水生哺乳动物。

The hippopotamus is known for its aggressive behavior. 河马以其攻击性行为而闻名。

The hippopotamus has thick, gray skin. 河马有着厚厚的灰色皮肤。