##  [hyphens: prefixes](/writing-tips-plus/hyphens-prefixes)

##  Avertissement

Ce contenu est offert en anglais seulement.

Follow these guidelines when deciding whether to use a hyphen after a prefix.

## *Ex, self, all* and *quasi*

Hyphenate nouns or adjectives beginning with the prefixes *ex* (meaning “former”), *self*, *all* and *quasi*:

- ex-wife
- ex-premier Getty
- self-control
- self-assured
- all-inclusive
- all-powerful
- quasi-judicial
- quasi-stellar

However, when *self* is the base word to which a **suffix** is added, do **not** hyphenate:

- selfish
- selfhood
- selfsame
- selfless

## SI/metric prefixes

Write SI/metric unit compounds as one word:

- centimetre
- gigagram
- kilokelvins
- milliampere

## Other common prefixes

Most words beginning with the following prefixes are written as one word: *after, ante, anti, bi, co, counter, de, down, extra, infra, inter, intra, iso, macro, micro, multi, over, photo, poly, post, pre, pro, pseudo, re, retro, semi, stereo, sub, super, trans, tri, ultra, un, under* and *up*.

- afterthought
- antecedent
- antiballistic
- bimonthly
- covalent
- counterclockwise
- decertify
- downturn
- extrasensory
- infrastructure
- interstellar
- intramural
- isometric
- macrocosm
- microscope
- multistage
- overestimate
- photovoltaic
- polyurethane
- postnatal
- preposition
- proconsul
- pseudonym
- readapt
- retroactive
- semiquaver
- stereophonic
- subspecies
- supernatural
- transcontinental
- triennial
- ultrasound
- unassuming
- underrate
- upswing
- upwind

However, there are many exceptions. Check the *Canadian Oxford Dictionary* when in doubt, and see below for three specific types of exceptions.

## Hyphenate for clarity

Use a hyphen when the word following the prefix begins with the same vowel as the one with which the prefix ends or when the compound’s appearance would be confusing without the hyphen:

- co-opt
- pre-eminent
- re-educate
- semi-invalid
- co-author
- de-icing

## Hyphenate to preserve a difference in meaning

In certain cases, use the hyphen to preserve a difference in meaning between the hyphenated and the solid compound:

- re-cover (cover again) vs. recover (get better, get back)
- re-create (create again) vs. recreate (take recreation)
- re-solve (solve again) vs. resolve (settle)
- re-sign (sign again) vs. resign (quit a job)

## Hyphenate before proper nouns and adjectives

Hyphenate a prefix joined to a proper noun or adjective:

- mid-July
- sub-Arctic
- neo-Christian
- trans-Siberian
- pro-Canadian
- un-American

**Exceptions:** transatlantic, transpacific

## Chemical terms

Hyphenate chemical terms preceded by an italicized prefix:

- *cis*-dimethylethylene
- *ß*-lactose

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Un outil créé et mis en ligne par le Bureau de la traduction, Services publics et Approvisionnement Canada

## Rechercher par thèmes connexes

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- [Punctuation](/fr/navigateur-navigator?search_api_fulltext=-&field_writing_tools=All&sort_by=views&f%5B1%5D=navigateur_navigator_english_theme%3A491#navigateur-navigator-resultats-results)
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- [Hyphenation](/fr/navigateur-navigator?search_api_fulltext=-&field_writing_tools=All&sort_by=views&f%5B0%5D=navigateur_navigator_english_theme%3A496&f%5B1%5D=navigateur_navigator_english_theme%3A498#navigateur-navigator-resultats-results)
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- [Prefixes and suffixes](/fr/navigateur-navigator?search_api_fulltext=-&field_writing_tools=All&sort_by=views&f%5B0%5D=navigateur_navigator_english_theme%3A500&f%5B1%5D=navigateur_navigator_english_theme%3A509#navigateur-navigator-resultats-results)

## Liens connexes

- [Writing Tips Plus](/fr/writing-tips-plus/index-fra) (page d’accueil)
- [Outils d’aide à la rédaction](/fr/outils-tools/index-fra)
- [Navigateur linguistique](/fr/navigateur-navigator) (permet de trouver rapidement des conseils linguistiques)
- [TERMIUM Plus®](http://www.btb.termiumplus.gc.ca/tpv2alpha/alpha-fra.html?lang=fra)