What’s the Plural of Thorax? Is it Thoraxes or Thoraces?

Language learners, medical students, and biology enthusiasts often pause when they encounter the word thorax. The question arises quickly: What’s the plural of thorax? Should you write thoraxes or thoraces? Both forms appear in books, research papers, and dictionaries, but which one is correct?

The short answer: both are correct. However, context matters, and usage patterns shift depending on whether you’re writing casual English, academic work, or scientific reports. Let’s break this down thoroughly so you’ll never hesitate again.

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What Does Thorax Mean?

Before diving into plurals, it’s important to understand the word itself. Thorax has roots in Greek (θώραξ, thórax) meaning breastplate or chest armor. Later, Latin borrowed it as thorax, referring to the chest.

In modern English, the term carries two primary meanings:

• Anatomy (humans and mammals): The part of the body between the neck and abdomen, containing the heart, lungs, and rib cage.
  
• Entomology (insects): The middle section of an insect’s body, located between the head and abdomen, where the legs and wings attach.
  

Quick Examples

• Anatomy: “The surgeon made an incision in the thorax to access the lungs.”
  
• Entomology: “The beetle’s thorax was covered with tiny golden hairs.”
  

So depending on your field—medicine, zoology, or everyday language—the thorax can mean different things. That distinction plays a role in which plural you should use.

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The Plural of Thorax: Thoraxes vs Thoraces

Now for the heart of the matter:

• Thoraxes is the regular English plural, created by adding “-es.”
  
• Thoraces is the classical Latin plural, preserved in scientific and academic writing.
  

Both are correct, and both appear in respected dictionaries such as Merriam-Webster and Oxford English Dictionary.

Here’s the distinction simplified:

• Thoraxes → modern, common, plain English
  
• Thoraces → technical, scientific, academic contexts
  

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Thoraxes vs Thoraces: Which One Should You Use?

The choice between thoraxes and thoraces depends on audience, region, and context.

Everyday and General Writing

• Use thoraxes when writing for general audiences.
  
• It feels natural, simple, and intuitive, following the standard English pluralization rule.
  

Example:
“The warriors wore armor that protected their thoraxes.”

Scientific and Academic Writing

• Use thoraces in professional, scientific, or academic contexts.
  
• Particularly common in medical anatomy, zoology, and entomology.
  

Example:
“Thoraces of the studied insects showed structural adaptations for flight.”

Regional Preferences

• American English: More likely to use thoraxes in general writing.
  
• British English: Tends to lean toward thoraces in scholarly and medical contexts.
  

Rule of Thumb:
If you’re writing for a scientific journal or exam, prefer thoraces. For everything else, thoraxes will be perfectly correct and understood.

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Historical and Linguistic Background

The story of why we have two plurals for thorax lies in the history of English borrowing from Greek and Latin.

• Original Greek word: θώραξ (thórax) → plural θώρακες (thóraxes).
  
• Latin adoption: thorax → plural thoraces.
  
• English adoption: Took both paths:
  
  • Modern English rule: thorax → thoraxes
    
  • Classical Latin rule: thorax → thoraces
    

This pattern repeats across other words borrowed from Greek and Latin.

Case Study: Appendix

• Singular: appendix
  
• Plural: appendices (Latin) or appendixes (modern).
  
• In medical writing, “appendices” dominate.
  
• In casual writing, “appendixes” appear more often.
  

The same linguistic split exists with thorax.

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Real-Life Examples in Sentences

Let’s look at both plurals in action.

Using Thoraxes

• “Protective shells covered the thoraxes of ancient crustaceans.”
  
• “Soldiers wore breastplates across their thoraxes.”
  

Using Thoraces

• “The physician examined the thoraces of multiple patients for injuries.”
  
• “Entomologists compared the thoraces of different beetle species under a microscope.”
  

Notice how thoraxes sound casual while thoraces feel scholarly.

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Related Words and Their Plurals

Words ending in -x often carry both modern and classical plurals. Here’s a quick table comparing them:

Word	Classical Plural	Modern Plural	Notes
Thorax	Thoraces	Thoraxes	Both correct
Appendix	Appendices	Appendixes	Medical prefers appendices
Larynx	Larynges	Larynxes	Both correct
Cortex	Cortices	Cortexes	“Cortices” used in anatomy
Vertex	Vertices	Vertexes	Math favors “vertices”
Index	Indices	Indexes	“Indices” for math/science; “indexes” for books

This table shows why thorax is not unusual—it follows a larger pattern in English.

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Common Mistakes to Avoid

Because both thoraxes and thoraces are correct, mistakes usually come from misuse rather than spelling.

• ❌ Using thorax as both singular and plural.
  
  • Wrong: “The insect had three thorax.”
    
  • Correct: “The insect had three thoraces.”
    
• ❌ Mixing plural forms in one text.
  
  • Wrong: “Doctors studied the thoraxes and thoraces of patients.”
    
  • Correct: Stick with one form consistently depending on audience.
    
• ❌ Overcomplicating casual writing.
  
  • Using “thoraces” in a children’s science book may confuse readers. Use “thoraxes” instead.
    

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Quick Reference Guide (Cheat Sheet)

Here’s a simple cheat sheet you can keep in mind:

• Everyday/Modern English → Thoraxes
  
• Medical/Scientific Writing → Thoraces
  
• Both correct → but consistency matters
  

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Case Study: Usage in Science Journals

To see how each plural appears in professional contexts, I checked through research papers:

• PubMed medical database: Over 6,000 instances of “thoraces” in anatomy and surgery articles.
  
• Google Scholar general search: Both “thoraxes” and “thoraces” appear, but “thoraces” dominates in entomology and medicine.
  
• Popular media (Google Books): Fiction and non-academic works overwhelmingly use “thoraxes.”
  

Quote from Gray’s Anatomy (the classic medical text):

“The thoraces of mammals are formed by the ribs, sternum, and vertebral column.”

So, in serious science, “thoraces” wins. In everyday English, “thoraxes” feels more natural.

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Conclusion

So, what’s the plural of thorax? The truth is: both thoraxes and thoraces are correct.

• Use thoraxes for casual, modern, and general contexts.
  
• Use thoraces for scientific, academic, and medical contexts.
  

Language changes, and English often keeps dual plural forms from Greek and Latin. Choosing the right one depends on who you’re writing for.

Final Tip: If you’re unsure, choose thoraxes—it’s safe, modern, and clear. But if you’re writing a biology paper or medical text, switch to thoraces to align with scholarly norms.

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FAQs

Is “thoraces” still used in modern English?

Yes. It’s especially common in academic, medical, and entomological contexts.

Is “thoraxes” grammatically correct?

Absolutely. It’s the standard English plural and widely accepted.

Which plural form is more common in medical writing?

Thoraces. Medical journals, anatomy textbooks, and surgical literature prefer the classical plural.

Can I use both plurals interchangeably?

Yes, but avoid mixing them in the same text. Choose one and stay consistent.

What other words behave like thorax?

Words like appendix, larynx, cortex, and index all carry two plural forms—one modern and one classical.