TIL the word octopus is not from Latin origin, it's Greek and it's plural is octopodes, but somewhere along the history of the English language, people decided to accept octopuses as the most common and correct plural of octopus. Therefor, octopi is considered incorrect.
It's the same with sheep. Many people believe, falsely, that the plural of sheep is sheeps. Just ask any drunk. Those with a classical education incorporating proto-Germanic literature, or a marketing degree, may feel an urge to amend this to sheepą and sheepō. Persnickety biologists may hide behind ovis which is problematic under any of the greco-latin declensions because sheep are mammals. I myself have adapted latterly to an abundance mindset and will refer in the plural simply to a flock and it follows that the singular of sheep is, quite naturally, monoflock. And I'm experimenting with a numerical trailer to express the cardinality, thus, flock(2)
It is considered incorrect, but it also sounds nice and forms a part of a growing number of terms being pluralized using -i, radiating out from cacti, it seems. I expect this trend will continue.
It doesn't sound nice to those who had at least a lick of Latin and Greek - so most Europeans.
The Romans conquered the Greeks militarily, but the Greeks conquered the Romans culturally. Saying "octopi" indirectly attempts to not acknowledge that.
I would say "octopuses" personally. "Octopodes" is more etymologically correct but you run the risk of not being understood, and "octopi", while in common usage, is etymologically wrong and people who are aware of this might look down on you slightly.
"Octopuses" is both understandable and correct etymologically since "octopus" is a normal English word.
Octopi is correct, in that it is an english language plural for octopus. It is not etymologically sound, certainly, as it's a latinate plural on a greek root.
So anyone telling you that any other form is wrong and insuating that 'octopi' is more correct is certainly asking to be mocked. But as we don't really do '-podes' in english, and "Octopusses" is a bit of a mouthful, I think we can accept any and all as more or less equally cromulent.
You're not wrong, though antipodes tends to pluralise antipode, rather than antipus!
That said, wikipedia mentions antipus or antipous may have been correct before the 16th century, and antipode is likely a sort of reverse de-pluralisation.
Tbh I'd understand it if you used all three forms. Octopuses is also etymologically incorrect, but the general public found it ok to use and it got generally accepted because people liked it. I don't see any reason for this to happen again with octopi, although now it might be more difficult.
Personally I'll use octopuses, just because I once confused octopi as a word for another species of the family octopodes belong to. Now I know it's a common plural, but it didn't sound like a plural to me back then.
I'd prefer to use octopodes, but I feel like this can too be confused with another species, and I don't want to sound all smart in saying it's actually a plural. Octopuses bypasses all that confusion, and probably everyone will understand that it's the plural of octopus, albeit some might have doubts whether it's the correct form or not.
