Plural of Hippopotamus: Understanding the Correct Form
Quick Answer
The plural of hippopotamus is hippopotamuses or hippopotami. Both are correct. In casual speech, most people just say hippos.
One: I saw one hippopotamus.
More than one: I saw three hippopotamuses.
Hippopotamus, Hippopotamuses, Hippopotami — See the Pattern
Look at these sentences. Can you see the pattern?
- One hippopotamus is in the river.
- Two hippopotamuses are in the river.
- The hippopotami at the zoo are very big.
- Look at all the hippos in the water!
Did you see it? When there is more than one hippopotamus, you can say hippopotamuses, hippopotami, or hippos. All three are correct.
| Singular (one) | Plural (more than one) |
|---|---|
| hippopotamus | hippopotamuses (standard English) |
| hippopotami (classical form) | |
| hippo | hippos (informal) |
Why There Are Two Correct Plurals
The word hippopotamus comes from Greek. It means “river horse.” Because it comes from another language, it has two ways to make the plural:
- English way: Add -es to the end → hippopotamuses
- Classical way: Change -us to -i → hippopotami
Other words do the same thing:
- cactus → cactuses or cacti
- octopus → octopuses or octopi
- hippopotamus → hippopotamuses or hippopotami
Easy way to remember: In everyday English, hippopotamuses is the safest choice. Hippopotami is also correct but sounds more formal. And most people just say hippos!
The Rule in One Line: Hippopotamus → hippopotamuses, hippopotami, or hippos — all correct.
How to Use Hippopotamuses in Everyday English
Here are sentences you might hear or use in everyday life:
- The zoo has three hippopotamuses in the new area. (talking about more than one)
- Hippopotami spend most of the day in water. (talking about all of them)
- We watched the hippos play in the river. (casual, everyday speech)
- Baby hippopotamuses can swim before they can walk. (a fun fact!)
- Are the hippos at this zoo friendly? (asking about specific ones)
You are doing great. Now let’s look at the mistakes many learners make.
Three Mistakes to Avoid With Hippopotamus
Even native speakers sometimes get confused with the plural of hippopotamus. So if you have made a mistake with this word, you are not alone!
✗ We saw three hippopotamus’s at the zoo.
✓ We saw three hippopotamuses at the zoo.
✗ The hippopotamusses are swimming.
✓ The hippopotamuses are swimming.
✗ I saw five hippopotamus in the river.
✓ I saw five hippopotamuses in the river.
How to remember: Never use an apostrophe (‘) to make a plural. And do not add extra letters — just add -es to hippopotamus, or change -us to -i.
Other words that work the same way: cactus → cactuses or cacti, fungus → funguses or fungi, octopus → octopuses or octopi.
Test Yourself: What Is the Plural of Hippopotamus?
Choose the correct answer for each sentence. Click Check to see if you are right.
1. We saw five _______ at the zoo yesterday.
2. The _______ in Africa live near rivers.
3. Look at all the _______ in the water!
4. Three baby _______ were born at the zoo this year.
5. The book had pictures of wild _______.
Keep Going — You Are Building Something
You just learned the plural of hippopotamus. That is one more tricky plural you will never get wrong again.
But what about another big animal — the rhinoceros? Do you say “three rhinoceroses” or “three rhinoceri“? (Only one of them is correct this time.)
Next lesson: What Is the Plural of Rhinoceros?
Sources
My name is Khamis Maiouf. I am the creator of the English Teacher Site, dedicated to providing valuable resources and insights for students around the world. With a passion for education and a commitment to helping students enhance their skills, I aim to make English teaching more effective and enjoyable for both educators and students.
