What is the plural of octopus?
Someone says octopi. Someone else corrects them. The strange part is that the person doing the correcting is usually wrong too.
It is one of the small reliable rituals of English. Someone says octopuses, someone else says “well, actually, it is octopi,” and everyone present quietly decides who is the cleverest person at the table. The ritual has a twist. The person doing the correcting is standing on the shakiest ground in the room.
The trouble with octopi
Octopi is built on an assumption: that octopus is a Latin word. Latin has a large group of nouns ending in -us that turn into -i in the plural, which is why fungus becomes fungi, alumnus becomes alumni, and cactus becomes cacti. Apply the rule and you get octopi. It feels educated. It sounds like you know something.
The problem is that octopus is not Latin. It is Greek. It comes from oktōpous: oktō, “eight,” and pous, “foot.” An eight-foot, or an eight-footer. The Latin rule is being applied to a word that never belonged to Latin, which makes octopi a bit like putting a French accent on a German word to sound sophisticated.
In fairness, the instinct is not baseless. Octopus arrived in English in the eighteenth century through the Latin of scientific naming, where it was the name of a genus. So the word did come in wearing a Latin coat. It simply was not a Latin word underneath it.
So should it be octopodes?
If you are going to insist on honouring the Greek, then honour it properly. The Greek plural gives us octopodes, which is said roughly “ok-TOP-uh-deez.”
It is defensible. It is also almost unusable. Say octopodes at dinner and you have not settled the argument, you have simply announced that you would like to keep having it. Dictionaries record the form, and essentially nobody reaches for it.
The boring answer is the right one
The best plural is octopuses.
It is not a lazy fallback or a concession to people who never studied Greek. It is the ordinary English plural, and octopus has been an ordinary English word for more than two centuries. English does not owe Greek or Latin anything here. We do not say pianoes because Italian would prefer it, and nobody demands forums be fora in casual speech. Words that live in English take English endings. That is not a decline in standards; it is what it looks like when a language actually owns a word.
Why we do this to ourselves
There is a name for this kind of error: hypercorrection. It is a mistake produced not by ignorance but by effort, by reaching for the fancier form because it feels safer. It is the grammatical version of overdressing.
The trap is everywhere once you see it. Platypus is also Greek, so platypi fails in exactly the same way. Ignoramus was never a Latin noun at all; it was a verb form meaning “we do not know,” so ignorami has nothing to attach to. Virus in Latin was a mass noun meaning poison, and it had no ordinary plural at all, which is why viruses is simply what English does with it.
The common thread is that each mistake is made by someone trying to be right. That is the whole comedy of it. The confident answer, the one that sounds too neat, is the one that deserves the most suspicion, which is a lesson OK teaches just as well.
So: octopuses, without apology. If someone corrects you, you may tell them the word is Greek. If they then say octopodes, they have earned it, and you should probably let them have the table.
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