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10.3. Spelling

10.3.1. Conventions

English spelling. Follow the standard usage of Britain and Ireland. As a general rule, the first spelling given on the Oxford Learner’s Dictionaries website, or on the Oxford Dictionaries Premium website (subscription required), should be followed (making sure in each case that the British English dictionary is selected).
-is-/-iz- spelling. Use the -is- spelling. Both spellings are correct, but this rule is to be followed for the sake of consistency in EU texts.
Note, however, that the names of bodies in other English-speaking countries retain the original spellings, e.g. US Department of Defense, Australian Labor Party. For international organisations, follow their own practice, e.g. World Health Organization. Follow the list in Annex 1 to the English Style Guide.
The -yse form is the only correct spelling for words such as paralyse and analyse.
When adding -able, drop a final silent -e at the end of the stem (debate – debatable, conceive – conceivable) unless it would change the pronunciation of the preceding consonant (changeable, traceable); the only common exceptions are sizeable and saleable (sizable and salable are US spellings).
Double consonants. Follow the convention of doubling a final -l after a short vowel on adding -ing or -ed to verbs (sole exception: parallel, paralleled) and adding -er to make nouns from verbs:
level, levelling, levelled, leveller
travel, travelling, travelled, traveller

Other consonants double only if the last syllable of the root verb is stressed or carries a strong secondary stress:

admit, admitting, admitted
format, formatting, formatted
refer, referring, referred


benefit, benefiting, benefited
combat, combating, combated
focus, focusing, focused
target, targeting, targeted

Exception: a few verbs ending in -p (e.g. kidnapped, worshipped, but not developed).

Judg[e]ment. Judgment is used in legal contexts, judgement in all other contexts.
Data-processing usage. Avoid the forms ‘input(t)ed’ and ‘output(t)ed’. Instead, use ‘input’ and ‘output’: e.g. ‘70 000 items of data were input last month’. However, note the verb ‘to format’ which takes the forms ‘formatted’ and ‘formatting’.
Accents and diacritics in personal names should be reproduced.

10.3.2. Tricky plurals

Follow the list below:

Singular Plural
addendum addenda
appendix appendices (books)
appendixes (anatomy)
bacterium bacteria
bureau bureaux
consortium consortia
corrigendum corrigenda
criterion criteria
curriculum curricula
embargo embargoes
focus foci (mathematics, science)
focuses (other contexts)
formula formulae (science)
formulas (politics)
forum forums (fora only in relation to ancient Rome)
genus genera
index indexes (books)
indices (science, economics)
maximum maxima (mathematics, science)
maximums (other contexts)
medium media (press, communications, IT)
mediums (life sciences, art)
memorandum memorandums or memoranda
minimum minima (mathematics, science)
minimums (other contexts)
moratorium moratoriums or moratoria
papyrus papyri or papyruses
phenomenon phenomena
plus pluses
premium premiums
referendum referendums or referenda
spectrum spectra (science)
spectrums (politics)
symposium symposiums or symposia
vortex vortices

10.3.3. Interference effects and in-house words, expressions and constructions

Especially in texts intended for the general public, care should be taken to avoid interference effects and the use of in-house words, expressions, constructions and meanings that are not generally recognised outside the EU institutions. Many of these are the result of confusion between English words and those from other languages (particularly French).

Frequently misused term Alternative
according to in accordance with
adequate appropriate
(legal) base (legal) basis
coherent consistent
debriefed briefed or informed
define establish or lay down
detached seconded
different various
disincentivise discourage
dispose of have
ensure provide for
foresee envisage or provide for
guarantee ensure
in case if
in case of in the case/event of
incentivise encourage
incite encourage
modalities detailed arrangements
modify amend
modulation reduction
nominate appoint
planification planning
precise specify
retain select

Please also see Sections 2.14 and 2.15 of the English Style Guide, How to write clearly and Claire’s Clear Writing Tips (for links, see Section 11, ‘Reference works’).

Last updated: 12.12.2022
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