“Gretchen: I think the best-known example of do you do the source language versus the target language in terms of plural in English is a certain little creature with eight legs.
Lauren: The octopus.
Gretchen: The octopus.
Lauren: Which I just avoid talking about in the plural at all to save myself a grammatical crisis.
Gretchen: I admit that I have also done this. If you were gonna pluralise “octopus” as if it’s English, it would just be “octopuses.” It’s very easy. But there’s a fairly long-standing tradition in English of when a word is borrowed from Latin to make the plural the actual Latin thing. Because, historically, many English speakers did learn Latin, and so you want to show off your education by using the Latin form even though it’s in English. So, if you’re going to pretend that “octopus” is Latin, then you wanna say, “octopi.” However, there is yet a third complication, which is that “octopus,” in fact, is actually Greek – “octo” meaning “eight” and “pus” meaning “feet. So, Greek does not make these plural by adding I to it. In that case, there has recently become popular a yet even more obscure and yet even more pretentious, to be honest, plural.
Lauren: Is there where you say, “octopodes”?
Gretchen: Well, this is where I used to say, “octopodes.” But I have recently learned that, apparently, it is, for maximum pretentiousness, /aktaˈpodiz/.
Lauren: You’ve out-pretentioused my out-pretentiousness.”