When was the last time you stumbled onto a word that didn’t end in “s” when it became plural? Or a plural that takes on a completely different spelling from the singular? The English language gives us some delightful little treats in the form of irregular plurals. These words with weird plural spellings should tickle your senses.
One octopus, two octopi, three octopi...
When it comes to the animal kingdom, many species have irregular plural spellings. Octopus and hippopotamus both get the i treatment, becoming octupi and hoppopotami respectively.
Elsewhere in the animal world, you have names that are the same word in singular and plural form. These are also known as “zero plurals.” One moose, three moose, ten moose. They’re all just moose. No "meese" or "moosi" to be found.
The same applies to deer, sheep, elk, walrus, antelope, fish, buffalo and salmon, just to name a few.
Sometimes you may not realize a word is plural unless you have knowledge of Latin. For example, data is actually the plural of datum (so you should be writing “data are” and not “is”).
Sometimes you have a choice when it comes to making a noun plural. That's the case with syllabus. If you want to talk about a stack of these collected on the first day of class, you can use either syllabi or syllabuses. Your choice.
This one may feel unnatural, but it is correct. If there’s a convention for people who are titled attorney general, it would be attorneys general, not attorney generals. It’s also senators elect, poets laureate, mothers-in-law and editors-in-chief.
Terms borrowed from other languages can break the plural rules as well. “Cul-de-sac” (French for bottom of the bag) is the singular, but if you’re winding around a neighborhood full of them, they’re “culs-de-sac.”