Hippocampus, a tiny organ in the brain - named after its resemblance to a tiny sea creature, the sea-horse (the genus of which is led to the original coinage of 'hippocampus') - has been some source of confusion.

Hippocampus = hippos (horse) + kampos (sea monster), effectively making it "sea monster horse"

However, there is also the word camp or campus, which means "flat land or field", which comes from Proto-Italic "kampo-"

Wiktionary entry for Hippocampus links the suffix to κάμπος which turns to be a synonym for "campus". "Sea monster" and "field" seem nowhere related in context. How did it come to be so?

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    I'm wondering if the origin is not horse + sea monster but rather horse + racetrack. The shape of the hippocampus in the brain is an incomplete oval that is somewhat like an ancient horse racetrack.
    – rajah9
    Commented Jul 23, 2019 at 12:41

2 Answers 2


You’re right that there is no relation between ‘sea-monster’ and ‘plain, field’ – the confusion is entirely due to how Wiktionary links function.


Κάμπος on the ground

It is important to note that the Wiktionary entry for κάμπος kámbos ~ kábos is for a Modern Greek word; in Modern Greek, κάμπος does indeed mean ‘plain, field’. I’m guessing this is probably a borrowing in Mediaeval or later times from Latin campus or perhaps from one of the Romance languages; it is, at any rate, a word that belongs in Modern Greek, and its meaning is the same as that found in Latin and her descendants.

Now, in Ancient Greek (AG), they actually had two words written κάμπος kámpos. One of them is the sea-monster word (see further below); the other one, while quite a rare word, is more like the modern one. It didn’t mean ‘plain, field’, though, but ‘horse-track, road for chariots’ (it was synonymous with the more common ἱππόδρομος hippódromos). Let’s call this horse-track word 1kámpos and refer to the sea-monster word as 2kámpos, just to be able to tell them apart more easily.

Ultimately, 1kámpos is cognate with Latin campus (and thus also with the Modern Greek word kámbos), but they are not the same. Both come from their respective (Italic and Greek) continuations of the Proto-Indo-European root *kh2em(p)- ‘bend, curve’, but their meanings diverged very early on, before the beginning of written records. Greek 1kámpos is a ‘twisty’ place – think of the Circus Maximus, a long, narrow, circular road that bends sharply at each end – while Latin campus is perhaps rather originally a ‘rolling’ or ‘undulating’ piece of land, as fields often tend to be.

I don’t know whether the Greeks borrowed Latin campus and 1kámpos eventually just quietly merged with that; or whether 1kámpos just died out on its own and disappeared completely, only for the Latin word to later be borrowed into Greek with its new meaning. It’s not unlikely that there is no way to tell at all. At any rate, the ‘ground’-related senses of the Modern and Ancient words written κάμπος are related to each other, but not to the sea-monster.


Κάμπος in the ocean

If you search Classical Greek dictionaries such as the ones provided by Perseus, the first and primary word written κάμπος that you’ll find is 2kámpos, the one meaning ‘sea-monster’ – written identically, but a different word altogether. This word was less rare than the horse-track word, but its etymology is also less straightforward and more uncertain.

There is a similar word κάμπη kámpē ‘caterpillar, fabled Indian monster’, which is surely related, but there isn’t much else to go on in terms of related words. Beekes suggests that the masculine form κάμπος may be derived from the feminine κάμπη under the influence of the somewhat similar (and masculine) κῆτος kē̂tos, a more generic term for any kind of monstrous being in the sea. In other words, the fabled Indian kámpē monster merged with the generic Greek kē̂tos monster to spawn a new kámpos monster who was closer in shape to the former, but in meaning to the latter.

Beekes also quotes two dialect forms, κέμμορ kémmor and γεμπός gempós, both of which have an odd kind of consonant change that looks very Pre-Greek in nature; so he eventually suggests that the word is probably of Pre-Greek origin. He tends to suggest Pre-Greek origins an awful lot, even where most others would disagree, but in this case, I’m inclined to agree with him.


Κάμπος in the brain

Regardless of its ultimate etymology, then, the 2kámpos is some kind of sea-monster. Slap a hippo- prefix on it, and it logically enough becomes a horsey sea-monster – more specifically, the ἱππόκαμπος hippókampos is a “monster with horse’s body and fish’s tail, on which the sea-gods rode”. A horse’s body and a fish’s tail. Well, that sounds sort of a bit like a description of a seahorse, doesn’t it? Like a griffin, but in the sea, and sort of matching an actually existing animal. Even the Greeks themselves noticed this, and they also used the word ἱππόκαμπος to denote the seahorse, though I don’t know if it was the common term for them or not.

The Romans later on borrowed the Greek term for the animal (though not, it seems, for the mythical sea-monster), as Latin hippocampus. So when – much later apparently – people started dissecting brains and found this little part that looked a bit like a seahorse, the Latin word they chose to name it after was hippocampus. Other names were proposed as well, but hippocampus, coined first by J.C. Aranzi in 1587 was the one that stuck.

  • Wiktionary... sigh
    – Mitch
    Commented Jul 23, 2019 at 12:47
  • @Mitch To be fair to Wiktionary, it did only do as it was told here. There is a link to a page named κάμπος, more specifically to the anchor named #Ancient_Greek on that page. Unfortunately, since the Ancient Greek meaning hasn’t been added to that page yet, there is no such anchor, so the link just goes to the page itself, which only contains the Greek (i.e., Modern Greek) entry. It’s confusing if you’re not familiar with the anatomy of Wiktionary entries, but if you are, it’s not – just a bit annoying that you go to a page to find something that hasn’t yet been entered. Commented Jul 23, 2019 at 12:52
  • The transition in meaning is still confusing. Perhaps both came about as homonyms/homophones. Perhaps drome and camp saw some interchangable usage as well. Thanks for your answer!
    – rolfk
    Commented Jul 23, 2019 at 15:36
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    @rolf Which transition do you mean? From ‘sea-monster’ to ‘seahorse’? Or from ‘seahorse’ to ‘part of the brain’? Or something else? I’ve updated the answer (actually rewriting and restructuring most of it) to give a more thorough overview of the different senses and how they relate to each other – I hope it’s clearer now. Commented Jul 23, 2019 at 16:52
  • @JanusBahsJacquet Thank you, again! The rewriting explains it much better. I suspect that kámpē~worm/caterpillar(monster?) has a part to play in the merging of contexts.
    – rolfk
    Commented Jul 24, 2019 at 8:46

The shape of the hippocampus may be like a seahorse, but it also might be like an oval horse and chariot track.


I'm going on an etymological limb here, and say that this region was named after an oval horse track rather than a horse seamonster. This begs the question as to why the Greeks named this region of the brain as hippocampus instead of hippodrome. (This is the secondary meaning in this answer, and I trust Janus's research.)

Inching out further on that limb. Perhaps the meaning of the campus in hippocampus is a field. And perhaps modern readers have inferred an incorrect back-formation.

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    This might have been the case, but for the fact that the area of the brain wasn’t named until the 1700s – not by the Ancient Greeks themselves. In Ancient Greek ἱππόκαμπος hippókampos refers only to the sea-monster (horse’s body, fish’s tail). It’s the word κάμπος kámpos itself that can also refer to a hippodrome. It would have been quite logical for it to be called a hippo-kámpos, but it doesn’t seem to have been. Commented Jul 23, 2019 at 15:43
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    According to Wikipedia, actually a bit earlier than the 1700s: “The earliest description of the ridge running along the floor of the temporal horn of the lateral ventricle came from the Venetian anatomist Julius Caesar Aranzi (1587), who likened it first to a silkworm and then to a seahorse”. (No source given, unfortunately.) Commented Jul 23, 2019 at 15:51
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    OED, "hippocampus, n.": "[1653 N. Culpeper tr. J. Vesling Anat. Body Man 60 Arantius gave the name of Hippocampus [L. hippocampi] or seahorse, and Silk-worm to them.] " Commented Jul 23, 2019 at 18:13

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