Tumour vs Tumor

Quick Answer

The fastest way to know which spelling to use.

The difference between tumor and tumour comes down entirely to geography and spelling rules.

If you are writing for an audience in the United States, the correct spelling is tumor (with an '-or' ending). If you are writing for an audience in the United Kingdom, Australia, or New Zealand, the correct spelling is tumour (with an '-our' ending).

Both words refer to the exact same thing: a swelling of a part of the body, often due to abnormal tissue growth. Neither spelling is grammatically incorrect, but using the wrong one for your target region can look out of place.

Tumour vs Tumor at a Glance

A side-by-side breakdown of the key differences.

Feature	Airplane (US)	Aeroplane (UK)
Standard Region	United States	United Kingdom
Spelling	T-U-M-O-R	T-U-M-O-U-R
Syllable Count	2 (TOO-mer)	2 (TYOO-mer)
Origin	Latin suffix (-or)	French influence (-our)
Meaning	Abnormal tissue growth	Abnormal tissue growth

American English: Tumor

How the word is used in the United States.

In the United States, "tumor" is the universally accepted spelling. It follows the standard American rule of using the "-or" suffix for words derived from Latin. It is used in medical contexts, cancer research, and everyday conversation.

Industry Standard

American medical professionals, oncologists, and cancer research organizations exclusively use "tumor" in their medical charts and clinical trials.

Media and Publishing

Major publications like The New York Times and The Wall Street Journal follow the "tumor" spelling.

British English: Tumour

How the word is used in the United Kingdom.

In the United Kingdom, "tumour" is the traditional and standard spelling. British English was heavily influenced by French, adopting the "-our" ending for many Latin-derived words. It is standard in British medicine, news, and literature.

Cultural Presence

The spelling is ubiquitous in British medical journals like The Lancet and in NHS (National Health Service) patient information leaflets.

Modern Usage

Though the root word is Latin, formal British writing relies on 'tumour' rather than the American simplification.

What Do Both Words Mean?

The definition remains exactly the same.

Despite the spelling difference, both "tumor" and "tumour" mean exactly the same thing. They refer to a solid or fluid-filled cystic swelling, often associated with cancer, that can arise in the body.

Core Definition

A swelling of a part of the body, generally without inflammation, caused by an abnormal growth of tissue.

Benign vs Malignant

Both words are used to describe growths that can be either benign (non-cancerous) or malignant (cancerous).

American English Usage

How Americans naturally use the word today.

In the US, "tumor" is used in almost every context, from casual conversation to technical medical reports. It is a staple in the healthcare, pharmaceutical, and life insurance industries.

Casual Conversation

"The doctor said the tumor was benign, so we are very relieved."

Technical Writing

"The drug was effective in shrinking the tumor in clinical trials."

Science Context

"The team is researching how the tumor metastasizes."

Entertainment Industry

"The MRI revealed a tumor on the patient's brain."

British English Usage

How Britons naturally use the word today.

In the UK, "tumour" holds its ground in literature, healthcare, and formal educational contexts. The 'our' ending is a natural grammatical rule for Britons.

Literature and Media

"The surgeon successfully removed the tumour from the patient's lung."

Everyday Conversation

"She was diagnosed with a brain tumour last week."

Hobbyist Contexts

"The vet found a small tumour on the dog's leg."

News and Journalism

"The new treatment has shown promise in fighting rare tumours."

Which Spelling Should You Use?

Deciding based on your audience.

The decision is entirely context-driven. If you are writing an email to an American colleague, use "tumor." If you are writing a postcard from London to your friends back in Britain, use "tumour."

Choose "Tumor" if:

You are writing for a US-based publisher, studying at an American school, or creating content primarily for an American audience.

Choose "Tumour" if:

You are submitting to a UK journal, writing for a British audience, or following Commonwealth English standards.

Formal and Professional Writing

What to do in business and academic contexts.

In highly formal writing, the safest approach is to adhere strictly to the regional standard. Both forms are correct, but consistency in grammar and spelling is paramount in professional contexts.

Business Contracts

International health insurance documents should define their style guide, usually selecting either US or UK English for suffix rules.

Academic Research

Scientific papers will typically use 'tumor' in US journals and 'tumour' in UK journals, especially when describing oncology results.

Pronunciation

The spelling change does not affect how the word is spoken.

The spelling difference doesn't change the spoken word; the '-our' and '-or' endings are pronounced identically.

Word	IPA	Syllables
Airplane (US)	/ˈtuːmər/	2 (TOO-mer)
Aeroplane (UK)	/ˈtjuːmər/	2 (TYOO-mer)

Both versions are pronounced with two syllables. The only difference is the first vowel sound: Americans use a pure 'oo' sound, while Britons add a 'y' sound before it, making it 'tyoo'.

Spelling Difference

A visual breakdown of the letters.

The core difference is the addition of the letter "u" before the "r".

Tumor

Tumour

The American version uses the '-or' suffix, tracing back to the Latin root. The British version uses the '-our' suffix, which is the standard rule for British English due to French influence.

Why Are the Spellings Different?

The history behind the transatlantic split.

1. The Latin Root

The word originates from the Latin 'tumor', meaning a swelling, derived from the verb 'tumere' (to swell).

2. The British French Influence

In British English, many words derived from Latin were adopted via French. The French suffix '-our' was anglicized to '-our', leading to the standard British spelling of 'tumour'.

3. Noah Webster's Reform

In the early 1800s, Noah Webster reformed American spelling. He preferred the '-or' suffix, tracing it directly back to the Latin '-or', establishing 'tumor' as the American standard.

Synonyms, Antonyms & Rhyming Words

Words related to, opposite of, and sounding like tumour/tumor.

Synonyms (Similar Meaning)

Antonyms (Opposite Meaning)

Rhyming Words (Sound Matches)

Learn More Rhyming Words

Example Sentences

See how both words function in original sentences.

Here are 30 original sentences using the American spelling, "tumor."

The doctor found a tumor on the scan.
The tumor was benign.
She had surgery to remove the tumor.
The tumor is growing rapidly.
He is undergoing treatment for a brain tumor.
The MRI revealed a tumor.
The tumor shrank after chemotherapy.
They are testing the tumor for cancer cells.
The tumor was pressing on the optic nerve.
She was relieved the tumor wasn't malignant.
The tumor mass was quite large.
The doctor biopsied the tumor.
The tumor markers in his blood are high.
He has a tumor on his lung.
The radiation targeted the tumor.
The tumor has metastasized.
The surgeon successfully removed the tumor.
The new drug is designed to shrink the tumor.
The tumor was detected early.
She is recovering from tumor removal surgery.
The tumor is inoperable.
The tumor board reviewed her case.
The treatment killed the tumor cells.
The tumor is affecting his vision.
They found a tumor on the pancreas.
The tumor was the size of a golf ball.
The biopsy confirmed the tumor was cancerous.
The tumor has stopped growing.
The patient is in remission after the tumor was removed.
The specialist studies tumor genetics.

Here are 30 original sentences using the British spelling, "tumour."

The doctor found a tumour on the scan.
The tumour was benign.
She had surgery to remove the tumour.
The tumour is growing rapidly.
He is undergoing treatment for a brain tumour.
The MRI revealed a tumour.
The tumour shrank after chemotherapy.
They are testing the tumour for cancer cells.
The tumour was pressing on the optic nerve.
She was relieved the tumour wasn't malignant.
The tumour mass was quite large.
The doctor biopsied the tumour.
The tumour markers in his blood are high.
He has a tumour on his lung.
The radiation targeted the tumour.
The tumour has metastasised.
The surgeon successfully removed the tumour.
The new drug is designed to shrink the tumour.
The tumour was detected early.
She is recovering from tumour removal surgery.
The tumour is inoperable.
The tumour board reviewed her case.
The treatment killed the tumour cells.
The tumour is affecting his vision.
They found a tumour on the pancreas.
The tumour was the size of a golf ball.
The biopsy confirmed the tumour was cancerous.
The tumour has stopped growing.
The patient is in remission after the tumour was removed.
The specialist studies tumour genetics.

Tumor in US English

Specific contexts, industry standards, and cultural data for the American spelling.

In the United States, "tumor" is the universally preferred spelling. It functions across multiple industries, from oncology to veterinary medicine. American style guides favor the '-or' suffix for Latin-derived words.

Medical & Healthcare

American oncologists, surgeons, and the National Cancer Institute (NCI) use 'tumor' in all clinical guidelines, medical charts, and patient communication.

Cancer Research

American research institutions and pharmaceutical companies use 'tumor' in clinical trial documents and medical journals.

Insurance & Law

American health insurance policies and legal documents regarding medical malpractice exclusively use the 'tumor' spelling.

Common American Phrases

• Brain tumor: A growth in the brain.
• Tumor marker: A blood test indicator.
• Tumor suppressor: A gene that stops cancer.
• Shrink the tumor: A treatment goal.

Tumour in UK English

Specific contexts, industry standards, and cultural data for the British spelling.

In the UK, "tumour" is the traditional spelling. The 'our' ending is a core grammatical rule in British English. It is used identically across medicine, research, and law.

Medical & Healthcare

The NHS and leading medical journals like The Lancet use 'tumour' in all clinical guidelines, medical charts, and patient communication.

Cancer Research

British research institutions and charities like Cancer Research UK use 'tumour' in their funding applications and published studies.

Insurance & Law

British health insurance policies and legal documents regarding medical malpractice exclusively use the 'tumour' spelling.

Common British Phrases

• Brain tumour: A growth in the brain.
• Tumour marker: A blood test indicator.
• Familial tumour: A genetic cancer risk.
• Remove the tumour: A surgical goal.

Related Suffix Vocabulary

Other words that differ in spelling rules.

US English	UK English	Meaning
Color	Colour	The property of light.
Flavor	Flavour	The taste of something.
Harbor	Harbour	A place for ships to dock.
Humor	Humour	The quality of being funny.

Other US–UK or vs our Differences

More words that change when you cross the pond.

Color vs. Colour

Americans spell it "color," while Britons spell it "colour."

Flavor vs. Flavour

The taste of food is "flavor" in the US and "flavour" in the UK.

Harbor vs. Harbour

A port for ships is "harbor" in America and "harbour" in Britain.

Humor vs. Humour

Being funny is "humor" in the US and "humour" in the UK.

Common Mistakes

Frequent errors writers make with these spellings.

Mixing spellings within the same document.

✓ Pick one regional standard and stick to it.

Why: Writing 'The tumor was benign, but the tumour was still removed' confuses the reader and breaks the consistency of your text.

Using "tumour" in an American academic paper.

✓ Use "tumor" for US-based journals and schools.

Why: American professors and publishers expect standard American English. Using the British spelling looks like a typo in this context.

Hyphenating the word ("tum-or").

✓ Always use a single, unhyphenated word.

Why: Modern English treats both 'tumor' and 'tumour' as solid compound words without hyphens.

Using "tumor" for a British children's book.

✓ Use "tumour" for UK audiences.

Why: British publishers strictly enforce regional spelling standards, especially in educational materials for kids.

Confusing the American and British spellings in global medical data.

✓ Remember the '-our' rule for the UK.

Why: In the UK, the 'u' is retained from the French influence. American English drops the 'u' in favor of the Latin '-or' root.

Assuming "tumour" is outdated or archaic.

✓ Recognize it as the current, active British spelling.

Why: Some Americans assume it's an old-fashioned word, but it is entirely modern and standard in the UK today.

Confusing the noun with the verb.

✓ Keep "tumor/tumour" (noun) separate from "swell" (verb).

Why: A 'tumor' is the thing itself. 'Swell' is the action. This is true in both US and UK English.

Forgetting that Canada usually aligns with the US.

✓ Use "tumor" for Canadian audiences.

Why: Despite being in the Commonwealth, Canadian English heavily favors American spellings for '-or' suffixes.

Using "tumorous" incorrectly.

✓ Ensure the adjective form follows the regional rule.

Why: If you write 'tumor' (US), you must also write 'tumorous' (US). If you write 'tumour' (UK), you must also write 'tumourous' (UK).

Using the wrong suffix rule in the UK.

✓ Remember that the UK uses the French '-our' suffix.

Why: British English was heavily influenced by French, leading to the adoption of the 'u' over the Latin '-or' in words like 'tumour.'

Writing for an International Audience

How to handle the split when writing globally.

If you are writing a blog, book, or manual for a global audience, you must pick a primary English standard. Most international organizations choose either US or UK English as their default and stick to it.

Pro Tip: Because American medical and scientific research dominates globally, many ESL learners are more familiar with "tumor." However, if your organization is based in Europe or the Commonwealth, "tumour" is the expected standard.

Memory Tip

An easy way to remember which spelling belongs to which country.

If you struggle to remember the difference, use this simple association trick:

America = Tumor

United Kingdom = Tumour

Think of the 'u' in 'Tumour'. The United Kingdom uses the 'u' in words like colour, flavour, and tumour. America drops the 'u' for a simpler spelling.

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Frequently Asked Questions

Quick answers to common questions.

Are 'tumor' and 'tumour' pronounced the same way?

They are pronounced very similarly, but with a key difference in the first vowel. Americans say 'TOO-mer', while Britons say 'TYOO-mer', adding a 'y' sound before the 'oo'.

Why does America use 'tumor' instead of 'tumour'?

In the early 19th century, Noah Webster sought to simplify American spelling. He preferred the '-or' suffix because it traced directly back to the Latin root 'tumor', whereas the British '-our' came from the French.

Is 'tumour' ever used in the United States?

It is very rare in modern American English. You might occasionally see it in historical contexts or older literature, but 'tumor' is the undisputed standard in the US today.

What about Canada and Australia? Which spelling do they use?

Canada generally follows the American spelling ('tumor'), though British spelling is also widely understood. Australia and New Zealand follow British English and use 'tumour'.

Is 'tumor' used for both benign and malignant growths in the US?

Yes. In the US, 'tumor' is used universally for both benign (non-cancerous) and malignant (cancerous) growths. There is no distinction based on the severity of the growth.

Which spelling is older, 'tumor' or 'tumour'?

The '-our' spelling is older in English, as the word entered the language via French. The '-or' spelling was later standardized in America by reverting to the original Latin root.

Should I use 'tumor' or 'tumour' in academic writing?

You should match the spelling to the regional standard of your audience or publisher. If you are writing for an American journal, use 'tumor'. For a British or international European journal, 'tumour' is preferred.

Does the rule apply to the adjective form as well?

Yes. The same rule applies to the adjective. Americans write 'tumorous' (ending in -or), while Britons write 'tumourous' (ending in -our).

Are there other words that follow this '-or' vs '-our' pattern?

Yes, many words follow this split, such as color/colour, flavor/flavour, harbor/harbour, and humor/humour.

Which word is more commonly used globally today?

Because of the dominance of American medical and scientific research, 'tumor' is recognized globally. However, 'tumour' remains the correct standard spelling in British, Australian, and New Zealand English.