If there’s one word in the English language that lacks consensus, it’s likely the plural form of octopus.
Octopuses
The most popular plural form is octopuses. If you ask any group of people on the street, “What do you call more than one octopus”, most of the people in that group will probably say octopuses.
Octopi
But a handful of those you ask will say octopi. In fact, some of them—if not all of them—will even say it in a ridiculing way, as a sleight to those who said octopuses. To them, octopus has an ending similar to cactus and fungus, whose plural forms are, respectively, cacti and fungi. Since the three have similar singular endings, they must have similar plural forms.
However, there’s a catch.
Cactus and fungus are both Latin-derived words, which explains the plural ending with an i. Octopus, on the other hand, is a Greek-derived word, so it wouldn’t make sense for a Greek word to take a Latin ending.
Octopodes
So, if we want to get technical about it because of its Greekness, the plural should be octopodes. It’s not pronounced like it looks though: The e isn’t silent but takes a long e sound.
Now, all that being said, all three versions have been around for over 100 years, even pushing 150 years. That means that by this point, they’re all English words, for all intents and purposes.
Even so, the most popular of the three is octoposes, by a long shot. Although octopi ruled the roost for a brief stint until about 100 years ago.
No matter what some people insist, octopuses is here to stay, and it will probably remain the more popular option for English speakers for some time to come.