河马在英语中的单词是'hippopotamus'。

Hippopotamus is a large herbivorous mammal native to sub-Saharan Africa. They are known for their massive size, with adult males weighing up to 1,500 kg. Despite their size, hippos are surprisingly agile and can run at speeds of up to 30 km/h. They spend most of their time in water, as it helps to regulate their body temperature and protects their sensitive skin from the sun.

The word 'hippopotamus' comes from the ancient Greek words 'hippos' and 'potamus', which mean 'horse' and 'river' respectively. This is a fitting name for this animal, as hippos spend much of their time in rivers and other bodies of water. Their massive size and powerful jaws make them one of the most dangerous animals in Africa, and they are responsible for more human deaths than any other large mammal on the continent.

In conclusion, the word 'hippopotamus' is a fascinating example of how the ancient Greeks named animals based on their characteristics and behaviors. Despite their size and strength, hippos are an important part of the African ecosystem, and their conservation is crucial to maintaining the balance of nature in this region.