Skip to content

Greek & Latin Endings – Plural Rules


Greek & Latin Endings

They are easy to spot because of how uncommon their base words are, and therefore implementing the formula is the easiest part!


by Brendan Bense

April 10, 2019


Don’t let the fancy title fool you. Greek and Latin endings aren’t as difficult as they appear. Unlike the last set of rules, these endings actually, well, follow rules. They are easy to spot because of how uncommon their base words are, and therefore implementing the formula is the easiest part! With all that said, don’t underestimate these words, as even native English speakers have a tendency to get them wrong. Show off your skills as you dive into our final episode of English plurals: Greek & Latin Endings.

A word of warning: this episode is not for the faint of heart. In fact, most of the words you encounter here are not found in beginner textbooks, or even intermediate ones. They contain the hardest plurals we’ve learned about thus far. So, if you’re just starting out learning English, it’s best to leave these rules for when you have already have an excellent grasp of the English language.

For some nouns ending in -us, change to -i to make them plural.


We know what you’re thinking: what singular nouns even end in -us? Well, buckle up. That’s going to be a theme for this episode. These words are pretty obscure and don’t come up often. The idea is to prepare you for all kinds of nouns, so you’ll always have a rule to point to! One of our favorite words for this rule is “cactus”. If you’ve never heard of the word cactus, think of the desert plant that has a bunch of spikes on it. They look like big green spiky tubes. Let’s follow the rule above! Since cactus ends in -us, change the -us to -i to make it a plural! Many cacti live in the desert. If we have more than one focus point, that means we have many foci. Yes, this this word looks extremely weird to spell. But it’s correct! Here’s an even weirder example: what do you think the plural of radius is? No, it isn’t radi, or radiuses. The correct plural is actually radii. Weird, isn’t it?

For every rule, as we have learned, there are exceptions. This rule is no different. Consider the word “octopus”. Many native English speakers would say that the plural for this animal is “octopi”. And, following the rule above, that sounds right. However, that is not the right plural. In fact, the correct plural would be octopuses or octopodes. Why is that? We don’t want to bore you, but octopus is a Greek-origin word, meaning its ending is different. Fascinating stuff. All this to say that these rules don’t appear out of thin air. They all have roots in past languages!

For some nouns ending in -is, change “is” to -es to make them plural.


We’re going to move on from rule ten to an equally challenging rule. Some nouns that end in -is must be changed to -es to make them plural. If you recall in our earlier rules, this one is similar to ES endings. Except, you’ll rarely see singular nouns that end in -is! There aren’t that many out there, but we don’t want you to be confused when you eventually run into them. If you are having a crisis, it means you are in an emergency situation. If you are having more than a single crisis, that sounds like a very bad day. It also means you are experiencing crises. The rule here is simple, but it is a bit daunting because it looks a little unnatural. Our first instinct would be to just add -es to make the word crisises. Except, of course, that’s not how English operates. Just remember that if you see -is, change the ending to -es instead of adding -es! Some other words include ellipses and analyses.

For some nouns ending in -on, change “on” to -a to make them plural.


This is it. Our final rule for English plurals! It’s about as hard as our previous two rules, so pay attention. Some nouns ending in -on need to be changed to -a to become plural. Simple enough, as we have a formula to follow. The trouble is that this rule is rare. Most nouns don’t end in -on. Further, we don’t often see the singular form of these nouns anyway! For example, the singular version of criteria (a word we see fairly often) is criterion. For this noun, we had to work backwards, because we don’t come across the word criterion much at all. Other words include taxa and phenomena!


Just because this is our final episode, doesn’t mean your study session is over! Why not test your skills with our deck on Greek & Latin Endings? FactSumo’s deck is designed with the student in mind: hone your skills, practice your weaknesses, and feel confident in plural endings! FactSumo is here to help with all your studying needs.

Feeling really confident? Good! That means you’re ready to tackle every deck we have for English plurals! Why don’t you head there now to see what’s in store for you? If you don’t think you’re ready to continue, no pressure! We want you to learn at your own pace. Either way, see you soon on FactSumo!