British and American English spelling of medical terms

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

Medical Writing: A Prescription for Clarity, 4th Edition, by Neville W. Goodman, Martin B. Edwards, Elise Langdon-Neuner, Andy Black

Concise Oxford English Dictionary

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By Jayne Fox, German-English medical translator and editor. I’d love to hear your thoughts on this article. Head over to Google+ or Twitter to continue the conversation!