If you’re a medical writer or translator, you’ll probably know that some medical terms are spelled differently in British and American English. The main differences relate to double vowels in British English, and certain word endings. Here’s a summary of the most important spelling differences, with notes on usage.
Vowels: ‘ae’ and ‘e’
Many medical terms spelled with ‘ae’ in British English are spelled with ‘e’ in American English, for example:
| British English | American English | Notes |
| aetiology | etiology | |
| anaemia | anemia | |
| anaesthetic | anesthetic | |
| caesarean | cesarean | Also: caesarian (UK) / cesarian (US) |
| defaecation | defecation | |
| dyslipidaemia | dyslipidemia | |
| glycaemic index | glycemic index | |
| gynaecology | gynecology | |
| haemoglobin | hemoglobin | |
| haemorrhage | hemorrhage | |
| ischaemic | ischemic | |
| leukaemia | leukemia | |
| orthopaedic | orthopedic | |
| paediatric | pediatric |
Vowels: ‘oe’ and ‘e’
Similarly, there are many medical terms spelled with ‘oe’ in British English that are spelled with ‘e’ in American English, such as:
| British English | American English | Notes |
| diarrhoea | diarrhea | |
| coeliac | celiac | |
| dyspnoea | dyspnea | |
| fetus or foetus | fetus | ‘Fetus’ is the preferred spelling in the BMJ and most other publications. Oxford Dictionaries lists foetus as a “variant spelling of fetus (chiefly in British non-technical use)”. |
| manoeuvre | maneuver | Note the ending also changes |
| oedema | edema | |
| oesophagus | esophagus | |
| oestrogen | estrogen |
Vowels/endings: ‘our’ and ‘or’
Words ending in unstressed ‘our’ in British English are usually spelled with ‘or’ in American English, for example:
| British English | American English | Notes |
| behaviour | behavior | |
| colour | color | |
| favour | favor | |
| humour | humor | However, humoral is used in both British and American English |
| labour | labor | |
| tumour | tumor |
Endings: ‘ise’ and ‘ize’
In British English, many verbs that end in ‘ise’ can also be spelled with the ending ‘ize’. For example, both realise and realize are correct. If you’re using a style guide, it may specify which form you should use. If not, it’s important to choose one form and use it consistently.
In American English, ‘realize’ and ‘recognize’ are correct but ‘realise’ and ‘recognise’ are incorrect.
However, in both UK and US English, some words can only end in ‘ise’, such as exercise, advise, revise and promise.
Endings: ‘lyse’ and ‘lyze’
In British English, many words ending in ‘lyse’ can also be spelled ‘lyze’, but some can only be spelled ‘lyse’, including analyse, catalyse and paralyse. In American English, these words all end in ‘lyze’.
| British English | American English |
| analyse | analyze |
| catalyse | catalyze |
| paralyse | paralyze |
Endings: ‘re’ and ‘er’
Most words ending in a consonant followed by unstressed ‘re’ in British English are usually spelled with ‘er’ in American English, such as:
| British English | American English | Notes |
| centimetre | centimeter | |
| centre | center | Use ‘Center’ in British English if it is part of an official name. |
| fibre | fiber | |
| litre | liter | |
| theatre | theater | |
| titre | titer |
Other spelling differences
There are a few other relevant spelling differences to note:
| British English | American English |
| ageing | aging |
| aluminium | aluminum |
| counsellor | counselor |
| dependants | dependents |
| fulfil | fulfill |
| intervertebral disc | intervertebral disk |
| leucocyte | leukocyte |
| license (verb), licence (noun) | license (verb and noun) |
| mould | mold |
| per cent | percent |
| practise (verb), practice (noun) | practice (verb and noun) |
| programme (not computer-related) | program |
Not just spelling
Spelling differences are only one aspect of the differences between American and British English. There are many other differences in usage, including verbs, prepositions, grammar and vocabulary. Lynne Murphy, an American linguist in the UK, writes an interesting and enlightening blog on this topic at ‘separated by a common language’.
Medical writing tips
If you’re not a native speaker of English, you might like our free email course on effective medical writing in English as a foreign language. Its ten short lessons guide you through the medical writing process, explain how to use tricky terms correctly and help you improve your medical writing.
German-English medical translation
See the German version of this article for additional notes on the German spelling of the terms listed above.
References and further information
Concise Oxford English Dictionary
https://en.wikipedia.org/wiki/American_and_British_English_spelling_differences
https://en.wikipedia.org/wiki/Comparison_of_American_and_British_English
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