河马用英语叫做 "hippopotamus"，蝴蝶用英语叫做 "butterfly"。

"Hippopotamus" 来自希腊语 "hippopotamos"，意思是 "马和水"。"Butterfly" 来自古英语 "butter-fleoge"，意思是 "黄油飞蝶"。

一些英文例句和中文翻译如下：

The hippopotamus is a large, semi-aquatic mammal native to Africa. (河马是一种原产于非洲的大型半水生哺乳动物。)

I saw a beautiful butterfly fluttering in the garden. (我在花园里看到一只漂亮的蝴蝶在飞舞。)

The hippopotamus is known for its large size and powerful jaws. (河马以其体型庞大和强劲的下颌闻名。)

The butterfly's wings are covered in colorful scales. (蝴蝶的翅膀上长满了五颜六色的鳞片。)