Hippopotami vs. Hippopotamuses vs. Hippos – Which is Correct?

When referring to more than one of the large, semi-aquatic mammals, all three terms—hippopotami, hippopotamuses, and hippos—are grammatically correct. Hippopotamuses is the most common and standard plural in modern English, hippopotami is a more formal or traditional plural derived from Latin, and hippos is a widely accepted informal shortening.

Hippopotami, Hippopotamuses, or Hippos – Which is Correct?

The choice between “hippopotami,” “hippopotamuses,” and “hippos” largely depends on context and desired tone. All three are valid plural forms for the animal known as a hippopotamus. The core difference lies in their origin and perceived formality.

• Hippopotamuses is the standard, anglicized plural, following typical English pluralization rules (adding -es). It is widely used in general communication and academic writing.
• Hippopotami is the classical plural, directly adopted from its Greek/Latin root. It carries a more formal, traditional, or even academic tone, similar to how “octopi” is used for “octopus.”
• Hippos is an informal, shortened version of “hippopotamuses” or “hippopotamus.” It is extremely common in casual conversation, popular media, and less formal writing.

While all are correct, “hippopotamuses” is generally the safest and most broadly accepted option in most contexts as of June 2026.

The Best Trick to Remember the Difference

To remember the difference, think about the origin of the word and its pluralization. The word “hippopotamus” comes from Greek, meaning “river horse.” Many words adopted into English from Latin or Greek have two plural forms: one following the original language’s rules and one following English rules.

The “Formality Rule” Trick:

• If you want to sound formal or traditional, use the Latin-sounding plural: hippopotami (ends like “alumni”).
• If you want to sound standard and clear, use the English plural: hippopotamuses (ends like “houses”).
• If you want to sound casual and quick, use the common abbreviation: hippos (just like “rhinos” or “elephants”).

Remember that the “us” ending in the singular “hippopotamus” often leads to either an “-es” English plural or an “-i” Latin plural, especially for words of classical origin.

Word	Part of Speech	Meaning	Example
Hippopotami	Plural Noun	Formal/traditional plural of hippopotamus.	“The wildlife documentary referred to the group as hippopotami.”
Hippopotamuses	Plural Noun	Standard, common plural of hippopotamus.	“Several hippopotamuses basked in the muddy river.”
Hippos	Plural Noun	Informal, shortened plural of hippopotamus.	“We saw a pod of hippos on our safari trip.”

How to Use Hippopotami

The term “hippopotami” is the classical plural form of “hippopotamus,” derived directly from its Greek etymology. Using “hippopotami” lends a more formal, traditional, or academic tone to your writing or speech. It is often preferred in scientific contexts, older texts, or when one wishes to evoke a sense of scholarly precision.

Example 1: “The paleontologist discussed the fossilized remains of ancient hippopotami found in the riverbed.”

Example 2: “In classical literature, descriptions of African wildlife sometimes referenced groups of hippopotami.”

Example 3: “The zoological society’s annual report detailed the reproductive cycles of various captive hippopotami.”

What are the different forms of Hippopotami?

“Hippopotami” is already a plural form. The singular form is “hippopotamus.” There are no other grammatical forms (tenses, comparative degrees) for this noun itself.

Etymology of the word Hippopotami

The word “hippopotamus” traces its roots to Ancient Greek: hippos (ἵππος), meaning “horse,” and potamos (ποταμός), meaning “river.” Thus, it literally means “river horse.” The plural form “hippopotami” directly reflects the Greek pluralization pattern for nouns ending in -os (which would become -oi in the nominative plural). This Latin-derived plural has been used in English for centuries, reflecting a period when classical plural forms were more common for words of Greek or Latin origin.

How to Use Hippopotamuses

“Hippopotamuses” is the most widely accepted and commonly used plural form in modern English. It follows the standard English pluralization rule of adding “-es” to nouns ending in “-us” (especially those not strictly adhering to Latin declensions in common usage). This form is appropriate for nearly all contexts, from everyday conversation and news articles to academic papers and formal presentations. It is clear, unambiguous, and avoids any perceived pretentiousness that some might associate with “hippopotami.” This plural also encompasses the informal usage of “hippos,” as “hippos” is simply a shortened form of the singular “hippopotamus” or the plural “hippopotamuses.”

Example 1: “Visitors watched as a pod of hippopotamuses emerged from the water.”

Example 2: “Conservation efforts are crucial to protect wild hippopotamuses from habitat loss.”

Example 3: “The documentary featured close-up footage of young hippopotamuses playing near their mothers.”

What are the different forms of Hippopotamuses?

“Hippopotamuses” is already a plural form. The singular form is “hippopotamus.” There are no other grammatical forms for this noun.

Etymology of the word Hippopotamuses

Like “hippopotami,” the word “hippopotamuses” also derives from the Greek hippos (“horse”) and potamos (“river”). However, “hippopotamuses” represents the anglicized pluralization of the word. As English evolved, many words borrowed from Latin and Greek began to adopt English pluralization rules rather than retaining their original classical forms. This shift made words more accessible and consistent with the broader patterns of the English language. “Hippopotamuses” became the more common plural by applying the standard “-es” ending, similar to how “octopuses” became more common than “octopi.”

Related Concepts

Understanding the broader linguistic principles behind these plural forms can help clarify their usage and similar words.

• Pluralization Rules: English has various rules for forming plurals, including adding -s or -es (e.g., cat/cats, box/boxes). However, for words derived from classical languages like Latin or Greek, there can be alternative plural forms that retain the original language’s rules (e.g., octopus/octopi, cactus/cacti, datum/data). “Hippopotamuses” follows English rules, while “hippopotami” follows classical ones.
• Formality in Language: The choice between “hippopotami” and “hippopotamuses” often reflects a difference in formality. Formal language tends to adhere to traditional or academic conventions, while informal language is more relaxed and common in everyday speech. “Hippos” is an excellent example of an informal shortening widely accepted in casual contexts.

Examples from Media and Literature

• “The children at the zoo were delighted to see the massive hippopotamuses wallowing contentedly in their enclosure.” (General news article, June 2026)
• “A recent scientific paper on African wildlife described the intricate social structures observed among groups of hippopotami.” (Academic journal, 2025)
• “My safari guide pointed out a group of hippos partially submerged, only their eyes and ears visible above the water.” (Travel blog, 2024)
• “The documentary narrator explained how young hippopotamuses learn to navigate the strong river currents from their mothers.” (Television documentary, 2026)
• “Ancient Egyptian hieroglyphs sometimes depicted hippopotami, revered and feared for their power.” (Historical text analysis, 2023)

Practice Exercises

Choose the correct word to complete the sentence.

1. The zoologist studied the aggressive territorial behaviors of adult __________.
2. For her casual blog post, she used the term __________ to describe the animals she saw on safari.
3. The academic lecture preferred the classical plural, referring to the large mammals as __________.
4. A pod of __________ can consume vast amounts of vegetation along the riverbanks.
5. The children’s book showed cartoon __________ playing in a muddy pool.

Answer Key

1. hippopotamuses (or hippopotami for a more formal tone)
2. hippos
3. hippopotami
4. hippopotamuses (or hippopotami for a formal tone, or hippos for an informal tone)
5. hippos

Hippopotami Synonyms

Synonym / Related Term	Definition / Usage
Hippopotamus	The singular form of the animal’s name.
Hippopotamuses	The standard, common English plural form.
Hippos	The informal, shortened plural form.
River horse	A literal translation of the animal’s Greek name, sometimes used descriptively.

Hippopotamuses Synonyms

Synonym / Related Term	Definition / Usage
Hippopotamus	The singular form of the animal’s name.
Hippopotami	The formal, traditional plural form.
Hippos	The informal, shortened plural form.
Pod of hippos	A collective noun phrase for a group of hippopotamuses.

Frequently Asked Questions

Question 1: Is “hippopotamuses” always the best choice?
While “hippopotamuses” is the most common and generally preferred plural in modern English, the “best” choice depends on your audience and the desired tone. For formal or academic contexts, “hippopotami” might be appropriate. For casual settings, “hippos” is perfectly acceptable.

Question 2: Can “hippos” be used in formal writing?
Generally, “hippos” is considered informal and should be avoided in highly formal academic papers, scientific reports, or official documents. In such contexts, “hippopotamuses” is the safer and more professional choice.

Question 3: Are there other words with similar pluralization quirks?
Yes, many words borrowed from Latin or Greek exhibit similar pluralization patterns. Examples include “octopus” (octopuses/octopi), “cactus” (cactuses/cacti), “fungus” (funguses/fungi), and “syllabus” (syllabuses/syllabi). The English plural is typically more common, but the classical plural often persists, especially in specific fields.

Conclusion

In the evolving landscape of the English language, “hippopotamuses,” “hippopotami,” and “hippos” all stand as correct plural forms for the majestic river horse. While “hippopotamuses” has emerged as the most widely accepted and standard plural in contemporary usage, “hippopotami” retains its place in more formal or traditional contexts, and “hippos” offers a convenient, informal alternative. Understanding these nuances allows you to choose the most appropriate term for any given situation.

Pro Tip: When in doubt, opt for “hippopotamuses” for clarity and broad acceptance. Reserving “hippopotami” for highly formal or specialized contexts and “hippos” for casual conversation demonstrates a strong command of linguistic register and enhances your professional reputation.