Tumor and tumour name the same thing: an abnormal mass of tissue that grows in the body and may be benign or cancerous. Tumour is the spelling used in British medical writing, while tumor is standard in American English, as in a scan revealing a small tumour to be monitored.
The core difference
Both spellings describe the same abnormal tissue growth; tumour is British and tumor is American.
- tumour — British spelling: Surgeons successfully removed the tumour before it could spread.
- tumor — American spelling of the same word: The scan revealed a small tumor that doctors wanted to monitor closely.
How to tell them apart
Both words descend from the Latin tumor, meaning a swelling, from tumēre, to swell — the same root that distantly gives English the word thumb. British English kept the fuller -our spelling, while American English shortened it to -or.
Because tumour is a medical term used in official reports, it is worth getting the regional spelling right in patient letters, referrals, and clinical writing aimed at a British audience.
