What’s the Plural of Apex: Understanding Variations in English Nouns

Apex, Apexes, Apices — See the Pattern

Look at these sentences. The key words are in blue:

• The mountain has one apex. (one top = singular)
• The mountains have three apexes. (more than one = plural)
• The scientist measured the apices of all the crystals. (more than one = plural, formal style)

Did you see the pattern? “Apex” means the very top or highest point of something. When you talk about more than one, you can say apexes or apices.

This happens because “apex” comes from Latin. In Latin, words ending in -ex change to -ices in the plural. But in modern English, you can also just add -es. Both ways are correct.

When to Use Apexes and When to Use Apices

Here is the simple rule:

Use “apexes” in everyday speaking and writing. It sounds natural and everyone will understand you:

• The roller coaster has three high apexes.
• The buildings had different apexes.

Use “apices” in science, maths, or very formal writing:

• The apices of the triangles were measured carefully.
• The leaf apices showed signs of damage.

Easy way to remember: If you are writing a school essay or chatting with friends, “apexes” is fine. If you are writing a science paper, “apices” sounds more professional.

How to Use Apex and Apexes in Everyday English

Here are sentences you might hear or use in daily life:

• The climber finally reached the apex of the mountain. (the very top of one mountain)
• She is at the apex of her career right now. (her highest point of success)
• The rooftops had sharp apexes that you could see from far away. (the pointed tops of several roofs)
• Lions are apex predators — they are at the top of the food chain. (“apex” used as a describing word)
• The apexes of the two towers looked beautiful at sunset. (the tops of two towers)

You are doing great. Now let’s look at the mistakes many learners make.

Two Mistakes to Avoid With the Plural of Apex

Even native English speakers get confused by Latin plurals sometimes — so if you find this tricky, you are not alone. These words come from an old language, and the rules feel strange in English.

How to remember: Words ending in -x need -es in the English plural (apex → apexes, box → boxes). The Latin plural changes -ex to -ices (apex → apices). There is no form like “apexs” or “apeces.”

Other words that follow this same pattern: index → indexes / indices, vertex → vertexes / vertices, vortex → vortexes / vortices.

Test Yourself: Apex, Apexes, or Apices?

Choose the correct answer for each sentence. Click Check to see if you are right.

Keep Going — You Are Building Something

You just learned the plural of apex. That is one more tricky plural you will never get wrong again.

But here is something interesting. You now know that “apex” becomes “apices” because it comes from Latin. But what about the word vertex? It ends in -ex too. Does it follow the same rule? And what is the difference between an apex and a vertex anyway?

Next lesson: What’s the Plural of Vertex?

Sources

1. Synonyms for apex.
2. Origin of the word apex.
3. Definition of apex.