Hippopotamus
The word hippopotamus arrived in English carrying a description that made perfect sense to the ancient Greeks who coined it — and almost no sense to anyone who has studied the animal since. From Greek *hippopotamos* (ἱπποπόταμος), the compound breaks down into *hippos* (ἵππος), meaning 'horse,' and *potamos* (ποταμός), meaning 'river.' The Greeks, encountering this barrel-shaped semi-aquatic megafauna for the first time along the Nile, reached for the nearest large animal they knew and concluded they were looking at a horse of the river.
The Greek Naming
The first surviving written account of the hippopotamus in Greek comes from Herodotus, writing around 440 BCE in his *Histories*. His description is a confident catalogue of error: he claims the animal has a horse's mane, cloven hooves, and a whinnying call. Almost none of this is accurate. The hippopotamus has essentially no mane, its toes are distinctly hippo-like rather than equine, and its vocalizations are a series of low honks and rumbles. What Herodotus almost certainly did was piece together a description from secondhand accounts and the general principle that large animals encountered near horses might reasonably be horse-adjacent.
Aristotle, writing in the fourth century BCE, gave a more careful anatomical account — noting the animal's true characteristics more accurately — but the name had already embedded itself in the language.
The Horse Element: *hippos*
The Greek *hippos* descends from the Proto-Indo-European root *h₁eḱwos, the ancient word for 'horse' that underlies equine terminology across the Indo-European family. Sanskrit preserves it as *aśva-*, Latin as *equus*, Old Irish as *ech*, and Old English as *eoh* (now obsolete in the common vocabulary, but present in place names). The shift from PIE *h₁eḱwos* to Greek *hippos* involves a well-documented pattern: the labiovelars (*kw* sounds) of PIE typically become plain velars or labials in Greek depending on environment, and in this case the labiovelar yielded the *p* of *hippos* — so what looks like a completely different word is in fact the same root wearing Greek phonology.
This makes the hippopotamus a distant linguistic relative of *equus*, and by extension of English words like equestrian, equine, and equerry (a royal horse official).
The River Element: *potamos*
Journey into Latin and English
Latin borrowed the Greek compound wholesale as *hippopotamus*, which is how learned European languages received it. The word appears in Latin texts by the first century BCE, used by authors describing Egyptian fauna. Medieval European writers who had never seen the animal reproduced it from classical sources with varying degrees of confidence.
English borrowed *hippopotamus* directly from Latin in the sixteenth century. The earliest recorded English use dates to around 1563, in a translation of natural history writing. The plural *hippopotami* follows Latin declension; the alternative *hippopotamuses* follows English convention. Both are current.
How Other Cultures Named It
The Greeks were not universal in their river-horse framing. The ancient Egyptians, who had lived alongside the hippopotamus for millennia, called it *dbt* or similar forms (the vocalization of ancient Egyptian is reconstructed), and did not reach for an equine comparison. To them the hippopotamus had its own identity, deeply embedded in religious symbolism — the goddess Taweret, protector of pregnant women and childbirth, was depicted with a hippopotamus body. Set, the god of chaos and disorder, was sometimes shown in hippopotamus form.
Modern Arabic uses *فرس النهر* (*faras al-nahr*), which translates as 'horse of the river' — a direct calque of the Greek compound, showing that Arabic adopted not just the word but the metaphor. Swahili uses *kiboko*, which carries no equine baggage at all and is simply the animal's own name in the regional tradition.
Cognates and Relatives
The *hippo-* prefix from Greek *hippos* generates a family of English words that share the horse root:
- Hippodrome — from *hippos* + *dromos* (course, track), originally a horse-racing venue - Philip — from Greek *Philippos*, 'horse-lover' (*hippos* + *philos*), a name borne by the father of Alexander the Great - Hippocrates — 'horse-power' or 'horse-ruler' (*hippos* + *kratos*) - Hipparchus — 'horse-commander' (*hippos* + *archos*), a name common in classical Greece and the title of cavalry officers
Through the PIE root *h₁eḱwos, the hippopotamus name connects back to Latin *equus* and all its English descendants: equestrian, equine, equerry (a royal horse official).
Modern Usage
The informal shortening hippo is attested from the mid-nineteenth century and has almost entirely displaced the full form in everyday speech. *Hippopotamus* persists in formal, zoological, and literary registers. The species currently recognised are *Hippopotamus amphibius* (the common hippopotamus) and *Choeropsis liberiensis* (the pygmy hippopotamus, whose genus name reaches for *choiros*, the Greek for pig, rather than horse — a more defensible anatomical comparison).
The word stands as a monument to the limits of ancient comparative zoology: a name coined in genuine descriptive good faith by writers who got the animal almost entirely wrong, and which has nevertheless survived intact for over two thousand years.