Hippopotami or Hippopotamuses: Which Plural Form Is Correct in English?

The short answer is that both “hippopotami” and “hippopotamuses” are acceptable plurals. Choosing one over the other sends subtle signals about tone, audience, and linguistic tradition.

This article dissects the history, grammar, style, and real-world usage of both forms so you can decide which fits your context.

Why English Has Two Plurals for Hippopotamus

English freely adopts Latin endings alongside regular ‑es plurals when a word enters from classical sources. The animal’s name comes from ancient Greek hippos (“horse”) and potamos (“river”), yet it reached English through Latin transcription.

Scholars in the 1600s preferred Latinized spellings to display erudition, so “hippopotami” gained early prestige. By the 1800s, popular science writing started favoring anglicized “hippopotamuses” for clarity.

Modern dictionaries now list both forms without labeling either as incorrect.

How Each Form Travels Across Registers

In peer-reviewed zoology journals, “hippopotamuses” appears in over 90 % of recent articles. Museum labels aimed at schoolchildren also favor the ‑es plural to avoid intimidating Latin endings.

Conversely, crossword puzzles and literary essays often choose “hippopotami” to create an elevated or whimsical tone. Travel brochures targeting wealthy safari-goers sometimes sprinkle “hippopotami” for exotic flavor.

Corporate style guides such as The Economist and The Chicago Manual of Style explicitly recommend “hippopotamuses” to maintain plain language standards.

Etymology Breakdown

Hippopotamus itself is a third-declension Latin neuter noun, whose plural is hippopotamī with a long “i”. English borrowed the word, then normalized the ending to ‑i for visual familiarity.

The Greek original, hippos-potamos, is masculine and would form its plural as hippos-potamoi, a form never adopted into English. This mismatch explains why “hippopotami” is technically a Latin-Latin hybrid, not a true Greek plural.

Understanding this backstory helps writers defend their choice when questioned by purists or editors.

Corpus Data: Real-World Frequency

The Google Books Ngram Viewer shows “hippopotamuses” overtaking “hippopotami” around 1960 and widening the gap ever since. COCA (Corpus of Contemporary American English) lists 1,034 tokens of “hippopotamuses” against 267 for “hippopotami” in news and academic prose from 1990-2019.

British National Corpus records a slimmer margin: 211 to 187, indicating stronger residual preference for the Latin form in UK English. Social media analytics from 2022 reveal “hippos” as the dominant shorthand, with the full plurals trailing far behind.

If your goal is to mirror prevailing usage, “hippopotamuses” is the safer data-driven pick.

Regional Variations

Canadian and Australian publications side with the American trend toward “hippopotamuses”. South African journals, steeped in British colonial lexicography, still lean on “hippopotami”.

In India, school textbooks standardize on “hippopotamuses”, yet competitive-exam coaching manuals revert to “hippopotami” to test Latin awareness.

Whenever your audience spans continents, specify the preferred form in a brief style note.

Technical Writing and Scientific Nomenclature

The International Code of Zoological Nomenclature (ICZN) does not regulate common names, leaving the choice to authors. Taxonomic papers therefore default to “hippopotamuses” to align with plain-language abstracts.

Captions in museum databases such as GBIF use “hippopotamuses” to facilitate global data interoperability. Grant proposals scored by interdisciplinary panels benefit from the same clarity.

If you cite classical texts, retain the original author’s spelling and add “[sic]” only if ambiguity risks misinterpretation.

Creative Writing and Literary Stylistics

Novelists exploit the two plurals as character markers. A pedantic professor might mutter about “hippopotami”, while a river guide shrugs about “hippopotamuses”.

Poets prize “hippopotami” for its trochaic swing and internal rhyme potential. Children’s authors favor “hippopotamuses” to keep sentences transparent.

Short stories can even alternate forms to signal shifting narrators or ironic distance.

Legal and Regulatory Documents

Contracts governing zoo acquisitions use “hippopotamuses” to avoid any risk of misreading. International wildlife treaties append glossaries that lock in “hippopotamuses” for cross-linguistic consistency.

Patent filings that reference animal models likewise prefer the anglicized plural. When precision overrides flourish, the regular form wins.

SEO Implications for Digital Content

Google’s keyword planner lists 27,100 monthly searches for “hippopotamuses” versus 8,200 for “hippopotami”. Crafting meta titles around the higher-volume term boosts discoverability without stuffing.

Yet long-tail queries such as “why is the plural of hippopotamus hippopotami” still drive traffic, so a balanced page can target both. Use H3 subheadings to isolate each spelling and signal topical breadth to search engines.

Internal links should anchor on the exact plural used in the target page to preserve keyword relevance.

Title Tag and Meta Description Examples

Title: “10 Astonishing Facts About Hippopotamuses You Never Knew”.

Meta: “Explore size, diet, and social behavior of hippopotamuses, plus the grammar debate over hippopotami.”

Both elements fit within 60 and 155 characters respectively, satisfying SERP best practices.

Academic Citation Styles

APA 7th edition leaves the choice to authorial preference, mandating only internal consistency within a paper. MLA 9th edition implicitly favors “hippopotamuses” by illustrating regular plural formation in its handbook.

Chicago style recommends checking the latest Merriam-Webster entry and defaulting to “hippopotamuses”. When quoting older sources, preserve original spelling without correction.

Teaching and Pedagogy

Elementary worksheets that introduce animal plurals stick to “hippopotamuses” to reinforce the general ‑es rule. High-school Latin courses leverage “hippopotami” as a mnemonic for second-declension masculine nouns ending in ‑us.

University linguistics seminars contrast the two forms to demonstrate morphological borrowing. Each level benefits from explicit comparison rather than rote memorization.

Pronunciation Guide

Hippopotamuses: /ˌhɪp.əˈpɒt.ə.mə.sɪz/ with primary stress on the third syllable. Hippopotami: /ˌhɪp.əˈpɒt.ə.maɪ/ ending with a diphthong “maɪ”.

Audio clips in online dictionaries favor the anglicized version, influencing learners worldwide. Podcast scripts should spell out the plural phonetically on first mention to prevent mishearing.

Common Myths Debunked

Myth: “Hippopotami is the only correct plural because it’s Latin.” Fact: Latin neuter plurals in ‑us are rare, and “hippopotamus” was never second-declension masculine. Myth: “Using hippopotamuses sounds childish.” Fact: Top-tier journals use it without stigma.

Myth: “The BBC mandates hippopotami.” Fact: BBC’s style guide lists “hippopotamuses” as preferred. Checking primary sources ends the debate faster than folklore.

Practical Decision Tree for Writers

1. Identify your primary audience. If children or global non-native speakers dominate, choose “hippopotamuses”. 2. Check the governing style guide; most prescribe the ‑es plural. 3. If no guide exists, default to corpus evidence favoring “hippopotamuses”.

4. In creative contexts where tone trumps rules, select the form that best characterizes the speaker. 5. Document your choice in a short style sheet so collaborators stay consistent.

Translingual Considerations

French uses “hippopotames”, Spanish “hipopótamos”, and German “Flusspferde”, none of which mirror the English dilemma. Multilingual packaging therefore benefits from the anglicized plural to reduce cognitive load.

Subtitles for nature documentaries standardize on “hippopotamuses” to align with dubbing scripts. When translating academic abstracts, retain the author’s original spelling to respect voice.

Marketing and Branding

A children’s toy line named “Happy Hippos” sidesteps the plural entirely. Luxury safari lodges trademark slogans like “Encounter Majestic Hippopotami” to evoke exclusivity.

Startup apps that crowd-source wildlife sightings opt for “hippopotamuses” in UI labels to ensure universal readability. A/B tests show 12 % higher click-through when the regular plural appears in call-to-action buttons.

Accessibility and Screen Readers

Screen readers pronounce “hippopotami” with a long “i” ending, which some listeners misinterpret as a possessive. Adding a comma after the word or using the ‑es plural reduces confusion.

Alt text describing a pod of hippopotamuses should state “group of hippopotamuses” instead of “hippopotami” for clarity. Testing with NVDA and JAWS confirms the smoother experience.

Future Trends and Corpus Shifts

Large language models trained on post-2000 web text overwhelmingly output “hippopotamuses”. As AI-generated content floods the web, this statistical preference may further entrench the regular plural.

Yet niche revival movements in online Latin forums keep “hippopotami” alive, ensuring dual survival. Predictive keyboards now suggest both forms, deferring to user history.