Interesting that the title doesn’t use “octopi”
"Although it is often supposed that octopi is the ‘correct’ plural of octopus, and it has been in use for longer than the usual Anglicized plural octopuses, it in fact originates as an error. Octopus is not a simple Latin word of the second declension, but a Latinized form of the Greek word oktopous, and its ‘correct’ plural would logically be octopodes."
https://en.oxforddictionaries.com/explore/what-are-the-plura...
but in all seriousness, language is a social construct. If someone says “octopuses” and everyone understands that they mean “more than one octopus”, then the communication was successful. And if enough people use it, then we’re looking at a successful new word. For better or worse.
(From Latin pes -> pedes)