Hippopotamuses or Hippopotami: What’s the Correct Plural of Hippopotamus?

When it comes to animals with unusual names, the hippopotamus always steals the show. But things get trickier when you’re talking about more than one. Should you say hippopotamuses or hippopotami? This isn’t just a funny animal plural—it’s a classic example of how Latin plurals in English can cause confusion. If you’ve ever paused before writing the plural of hippopotamus, you’re not alone.

The truth is, both hippopotamuses and hippopotami are technically accepted, but there’s a twist. One follows English irregular plural rules, while the other is rooted in Latin word origins. Understanding the etymology of hippopotamus helps explain why both forms exist and why some people lean toward one over the other. Plus, knowing the correct plural of hippopotamus can keep your grammar sharp—especially when you’re writing about animal names in English or trying to avoid common English grammar mistakes.

In this post, we’ll break down the hippopotamus plural form, explore the quirks of Greek and Latin word origins, and explain how to use both versions correctly in a sentence. Whether you’re a language enthusiast, a student, or someone who just loves learning about funny animal plurals, we’ve got you covered. Let’s dive into the wild world of hippos vs hippopotami and settle this once and for all.

What’s the Plural of “Hippopotamus”?

The correct plural form of hippopotamus is:

Hippopotamuses

That’s right. Just like most English nouns, you add -es to make it plural. It follows the same rule as bus → buses or octopus → octopuses (yes, not octopi—we’ll explain that too!).

But here’s where things get tricky. Some people also use:

Hippopotami

Technically, hippopotamuses is the correct modern English plural. Hippopotami is acceptable, but it’s considered poetic or outdated.

Why Are Both “Hippopotamuses” and “Hippopotami” Accepted?

It Starts with the Word’s Origin

The word hippopotamus comes from ancient Greek, not Latin:

• hippos = horse
• potamos = river
  Together: “river horse”

Later, the Romans borrowed it into Latin, and from there, English adopted it.

Now, in Latin, many words ending in -us form their plural with -i (like cactus → cacti). So, people assumed hippopotamus followed the same rule.

But here’s the truth:

“Hippopotamus” is Greek in origin, so technically, its Latin-style plural “hippopotami” is a hypercorrection.

Still, language evolves—and so both forms entered modern English.

Dictionary Stance

Here’s what major dictionaries say:

• Merriam-Webster: Lists both hippopotamuses and hippopotami as correct.
• Oxford English Dictionary: Agrees, but marks hippopotamuses as the primary form.
• Cambridge Dictionary: Recommends hippopotamuses for general use.

Which Is More Common: Hippopotamuses or Hippopotami?

To settle this, let’s look at real-world data.

Usage in Books and Speech

According to the Google Ngram Viewer, which tracks word use in books over time:

• Hippopotamuses is far more common since the 20th century.
• Hippopotami peaked in the 1800s but dropped sharply.

In modern writing and speech, hippopotamuses dominates.

Style Guides

Most English writing guides prefer:

• “Hippopotamuses” for formal, academic, and professional settings.
• “Hippopotami” may appear in poetry, humor, or older literature.

“Hippopotamuses sounds more natural and is widely understood.”

What Is a Hippopotamus?

The hippopotamus is a large, mostly herbivorous mammal that lives in rivers and lakes across sub-Saharan Africa.

Quick Facts:

• Weight: Up to 4,000 pounds
• Length: About 11 to 17 feet
• Speed: Can run up to 19–25 mph on land
• Known for: Aggressive behavior, yawning displays, loud grunts, and spending most of their day in water

Hippos are one of the most dangerous animals in Africa, responsible for more human deaths per year than lions or crocodiles.

What’s the Difference Between “Hippo” and “Hippopotamus”?

Hippo is just a shortened, informal version of hippopotamus.

Word	Formality	Use Case
Hippopotamus	Formal	Academic writing, scientific documents
Hippo	Informal	Everyday speech, kids’ books, social media

Both refer to the same animal. The only difference is tone.

What’s the Plural of “Hippo”?

Easy:

Hippos

This follows standard English plural rules.

So:

• One hippo
• Two hippos
  

Unlike hippopotamus, there’s no debate here. Hippos is the only correct plural of hippo.

Using “Hippopotamus” and “Hippo” in Singular Sentences

Let’s look at how these words are used in real-life examples.

Hippopotamus (Singular)

• “The hippopotamus is the third-largest land mammal in the world.”
• “A single hippopotamus can hold its breath for up to five minutes.”

Hippo (Singular)

• “Look at that hippo floating in the river!”
• “The baby hippo followed its mother closely.”

Using “Hippopotamuses,” “Hippopotami,” and “Hippos” in Plural Sentences

Hippopotamuses

• “Hippopotamuses are surprisingly fast runners.”
• “Many hippopotamuses gathered around the riverbank at sunset.”

Hippopotami

• “Poets often describe hippopotami as ‘majestic water beasts.’”
• “In old texts, you’ll sometimes read about ‘hippopotami in the Nile.’”

Hippos

• “We spotted three hippos on our safari tour.”
• “Hippos are more aggressive than they look.”

Word Origin and Etymology of “Hippopotamus”

Let’s break down the word:

Greek Root	Meaning
hippos	horse
potamos	river
hippopotamos	river horse

It entered English from Latin, but the base structure is still Greek.

That’s why the Latin-style plural (hippopotami) isn’t technically correct—but still survived in English due to stylistic use in literature.

What Do You Call a Group of Hippopotamuses?

This is where English gets fun.

Collective Nouns for Hippos:

• A bloat of hippopotamuses
• A pod of hippopotamuses
• A herd of hippopotamuses

“Bloat” is the most colorful and commonly used collective noun—possibly inspired by their bulky appearance.

Example:

• “A bloat of hippos gathered near the watering hole.”
• “We watched a herd of hippopotamuses wade through the marsh.”

Final Word: Which Plural Should You Use?

So, when should you choose one over the other?

Use Hippopotamuses:

• In formal writing
• In academic work
• When clarity is key
• In news articles or factual reports

Use Hippopotami:

• For literary effect
• In humor or poetry
• When aiming for an old-fashioned or classical feel

Tip: If you’re ever unsure, just use hippopotamuses. It’s always safe.

Quick Comparison Table

Form	Number	Formality	Recommended Use
Hippopotamus	Singular	Formal	Scientific, educational writing
Hippo	Singular	Informal	Speech, blogs, children’s books
Hippopotamuses	Plural	Standard	All modern contexts
Hippopotami	Plural	Archaic/Literary	Poetry, stylized writing
Hippos	Plural	Informal	Conversation, casual content

FAQs

Is “Hippopotami” grammatically correct?

Yes, but it’s considered a Latin-influenced plural and is less common in modern usage.

Which plural is more accepted in the US?

Hippopotamuses is more widely accepted in US English.

Can I use “hippos” in an essay?

Only if the tone is informal. Otherwise, use “hippopotamuses.”

Is “hippopotami” wrong?

No, but it’s seen as old-fashioned or poetic rather than standard.

What do you call a group of hippos?

A bloat, a pod, or a herd—all are correct, but “bloat” is the most popular.

Conclusion

The plural of hippopotamus may look confusing, but the answer is simple once you know the facts. Hippopotamuses is the correct and modern plural, and it’s what you’ll find in textbooks, news articles, and scientific papers. Hippopotami, while not technically wrong, is more of a stylistic choice than a grammatical one.

And remember—whether you’re writing about one hippopotamus, a dozen hippos, or a whole bloat of hippopotamuses, the key is to pick the word that fits your tone, audience, and purpose.