Plurals for hippopotamus and octopus

It is a popular and well-known fact that the correct plural for “octopus” is not “octopi,” but “octopuses” or “octopodes.” This is because the word “octopus” is Greek in origin, not Latin, and the Greek word for the word “pos” (foot) is “podes.”

Here’s my question: If it is incorrect to pluralise “octopus” as “octopi,” then why is it okay to pluralise “hippopotamus” as “hippopotami?” The OED says that this is an acceptable plural.

The word “hippopotamus” is also Greek in origin. It comes from “hippos ho potamios.” In Greek, “hippos” means “horse,” and “potamos” means “river.” The plural of “hippos” is “hippoi,” as I recall.

So shouldn’t the plural be “hippoipotamus” or maybe “hippopotamoi?”

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The Grey Literature

This is the personal blog of Benjamin Gregory Carlisle PhD. Queer; Academic; Queer academic. "I'm the research fairy, here to make your academic problems disappear!"

10 thoughts on “Plurals for hippopotamus and octopus”

  1. I have been asking myself the same question for a while now. I think that “hippopotamoi” would be “horse of the rivers”. I’d suggest “hippoipotamus”. Or maybe “hioppoipotamoi”.

    Je me pose la même question pendant beaucoup de temps. Je pense que “hippopotamoi” serait “cheval des fleuves”. Je suggerais “hippoipotamus”. Ou peut-être “hioppoipotamoi”.

  2. Hmph. I just plugged “hippopotamus” into Google Translate and it said “Ιπποπόταμος”. Then I did the same thing for “hippopotamuses” and it said “Ιπποπόταμοι”. So, there you have it, in Greek.

    Hmph. Je viens de mettre “hippopotame” dans Google Translate et il a dit “Ιπποπόταμος”. Puis, j’ai fait la même chose pour “hippopotames” et il a dit “Ιπποπόταμοι”. Voilà, en grec.

  3. Well there you go!

    I wonder if it would take the internal pluralisation if you were literally saying “horses of the river”—”hippoi ho potamios” ?

  4. Well, “the horses of the river” in Greek would be “oi ippoi apo tou potamou”. Literally, “The horses from the river”. I guess “hippopotamus” is a compound word that is pluralized as its own entity.

  5. ‘Hippoipotamus’ is strictly correct, I believe, but since many Greek words were incorporated into Latin in Ancient times, words with Greek roots can also be used with Latin inflections. The same can be said for ‘hippocampus’, of which there are two in the brain, so these should perhaps be known as the ‘hippoicampus’ but here too one sees ‘hippocampi’ written.

  6. I’ve been thinking about this for a few minutes now and I believe Greek or not it’s hippos this solves all problems

  7. I have been saying that it is the horses that are plural, not the river. So hippoipotamus it should be.
    Eric Partridge argued that the plural of lion was lion. The ‘s’ is incorrect.

  8. I had had this same question for a long time. People would tell me that the reason that octopi wasn’t a proper plural was that we had gotten the word octopus from Greek. But this, of course, wasn’t true. If we had, it would almost certainly be octopous, which is essentially how it is spelled in Greek. We got it from Latin which got it from Greek. So I always wondered why we didn’t apply the same standard to hippopotamus which is also a word we got from Latin which got it from Greek. It turns out that the real answer is this: in Latin, the correct plural of octopus is not octopi. Not all nouns ending in -us become -i in the plural. Hippopotamus does, but octopus doesn’t. So what is the proper Latin plural of octopus? Well, in Latin, it’s octopodes, which, of course, they took from the Greek. So that’s why octopi is incorrect. It’s not the Latin plural. It’s just a bad guess at the Latin plural.

  9. I espouse “hippopotamoi”, because “hippopotamos”, being a contraction, I would inflect as a single unit, and not pluralize in the middle of the word.
    But what about the plural of “rhinoceros”? This is another one that’s from Greek but came through via Latin; so it becomes a question of how far back in time we want to go before pluralizing it. Treating is as an English word, you could say “rhinoceroses”; treating it as a Latin word, you could say “rhinocerotes” (and there is some, albeit archaic, precedent for this); but should we take it all the way back to Greek to pluralize it? Etymonline says the Latin word is from Greek “rhinokeros”, from “rhinos” + “keras”. So…. would I say “rhinocerata”? Or, when the “keras” somehow got changed to “-keros”, did that change the declension of the word??

  10. These are the important questions. We can look up how to pluralize the roots, but once the word becomes modified on its journey into Latin, how is the plural modified? And why didn’t anyone think of this and write it down the second the word was coined? I do feel mildly foolish saying octopodes when I don’t say octopous. would the latin equivalent be octopedes?

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