British spelling of tumor; an abnormal growth of tissue resulting from uncontrolled cell division, which may be benign or malignant.
From Latin 'tumor' meaning 'swelling', derived from 'tumere' (to swell). The medical term was adopted directly from Latin in the 14th century, maintaining the classical spelling in British English while American English simplified it to 'tumor'.
The word tumour literally just means 'swelling' in Latin, showing how ancient physicians described what they could observe before understanding cellular biology! The British retention of the 'ou' spelling reflects the ongoing influence of Latin medical terminology, while the American 'tumor' represents the practical simplification trend in American English.
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