That's a Wrong Word: Octopi
by Aarushi Agni, Assistant Editor
Quick, what’s the plural of octopus? Did you say octopi? You’re not alone.
Contrary to popular assumption, the English plural of octopus is “octopuses.”
The word octopus came into English usage in the mid-1700’s and thus took an English plural, making it “octopuses.” But at the time, there was a grammatical movement to use Latin endings of words, making the plurals of words that end with –us end with –i. (For example, the plural of the word syllabus is syllabi.)
Later, grammarians saw the error in that fix: “octopus” actually comes from Greek rather than Latin. So, they pushed for usage of the Greek plural instead: octopodes. This word is so rarely used that spell-check corrects it.
“They all forgot one thing!” said Kory Stamper, associate editor at Merriam Webster, “Whenever a word from a foreign language enters English, it becomes an English word and gets inflected just like other English words. So ‘octopuses’ is just fine!”
Meanwhile, “octopi” has been used so commonly in so many different contexts that it is now also considered acceptable.
[Source: Merriam Webster Online, New Oxford American Dictionary]