The dé- / dés- prefix is French's primary tool for expressing reversal: undoing an action, removing a state, separating from something. Where English uses un- (untie), de- (defrost), or dis- (disagree) depending on the word, French uses a single prefix that absorbs all three functions. Défaire (undo), décongeler (defrost), désaccord (disagreement) all share the same morpheme.
This page covers the spelling rule (dé- vs dés-), the three main semantic types of dé- formations, and a handful of irregular cases where the prefix has lost its reversal meaning.
The spelling rule: dé- vs dés-
The prefix has two forms, distributed phonologically.
- Dés- before a vowel (including the silent h-). The -s- prevents the two vowels from running together and preserves the closed /e/ of the prefix.
- Dé- before a consonant.
| Form | Before | Examples |
|---|---|---|
| dés- | vowel or silent h- | désaccord, désorganiser, désintéresser, désespérer, désharmonie, déshabiller |
| dé- | consonant | défaire, démonter, déconnecter, déboucher, déranger |
The h- in French is either silent (h muet, allowing liaison and elision) or aspirated (h aspiré, blocking liaison). The dés- form appears before h muet — déshonneur, déshabiller, déshydrater, déshumaniser. Before an aspirated h-, you would use dé-, but the productive dé- forms with aspirated h- are rare.
Il faut déshabiller le bébé avant le bain.
You have to undress the baby before the bath.
Cette région a été déshumanisée par la guerre.
This region has been dehumanized by the war.
Je suis en désaccord total avec sa décision.
I completely disagree with his decision.
Sense 1: undo, reverse an action
The most common reading. The dé- prefix attaches to a verb and produces a new verb meaning "undo what V does."
| Base verb | Dé- verb | Meaning |
|---|---|---|
| faire (do, make) | défaire | undo |
| monter (assemble, go up) | démonter | disassemble, take apart |
| plier (fold) | déplier | unfold |
| nouer (tie) | dénouer | untie |
| charger (load) | décharger | unload |
| brancher (plug in) | débrancher | unplug |
| connecter (connect) | déconnecter | disconnect |
| boutonner (button) | déboutonner | unbutton |
| verrouiller (lock) | déverrouiller | unlock |
| geler / congeler (freeze) | dégeler / décongeler | thaw / defrost |
| boucher (block) | déboucher | unblock, uncork |
| visser (screw in) | dévisser | unscrew |
| chausser (put shoes on) | déchausser | take shoes off |
| habiller (dress) | déshabiller | undress |
| maquiller (put makeup on) | démaquiller | remove makeup |
| coller (glue, stick) | décoller | unstick, take off (of a plane) |
Tu peux déboucher la bouteille de vin, s'il te plaît ?
Can you uncork the wine bottle, please?
J'ai dû démonter le meuble pour le faire passer par la porte.
I had to disassemble the piece of furniture to get it through the door.
N'oublie pas de te démaquiller avant de te coucher.
Don't forget to take your makeup off before going to bed.
L'avion va décoller dans quinze minutes.
The plane is going to take off in fifteen minutes.
The reversal logic is intuitive: whatever the base verb does, the dé- verb undoes. If you have plié (folded) the paper, you déplie (unfold) it; if you have branché (plugged in) the lamp, you débranche (unplug) it.
Décoller and décollage: the metaphor extended
Note décoller in the table above: literally "unstick," it has extended to mean take off (of an airplane). The metaphor is the plane unsticking from the ground. The noun décollage (takeoff) follows. This kind of metaphorical extension is common with dé- verbs.
Le décollage a été retardé à cause du brouillard.
The takeoff was delayed because of the fog.
Sense 2: remove, separate from
Sometimes the dé- prefix means "remove the thing the base noun names" rather than "undo the action the base verb names." The prefix attaches to a noun stem and produces a verb meaning "remove that thing."
| Base noun | Dé- verb | Meaning |
|---|---|---|
| poussière (dust) | dépoussiérer | remove dust, dust off |
| bois (wood, forest) | déboiser | deforest |
| os (bone) | désosser | debone |
| plume (feather) | déplumer | pluck (feathers) |
| graisse (grease) | dégraisser | degrease |
| neige (snow) | déneiger | clear snow |
| givre (frost) | dégivrer | defrost (a freezer, a windshield) |
| limite (limit) | délimiter | delimit, set boundaries |
Il faut bien dégivrer le pare-brise avant de partir.
You have to defrost the windshield properly before leaving.
Je dépoussière l'étagère une fois par semaine.
I dust the shelf once a week.
On a déboisé des hectares entiers pour cette plantation.
They deforested entire hectares for this plantation.
The pattern is productive in technical and specialized vocabulary — agriculture, butchery, technology — and learners encounter it most in cooking and environmental contexts.
Sense 3: negation (attached to adjectives and nouns)
When dé- / dés- attaches to a noun or adjective, it often produces a negative or opposite term. This is closer in spirit to English dis-.
| Base word | Dé- form | Meaning |
|---|---|---|
| agréable (pleasant) | désagréable | unpleasant |
| accord (agreement) | désaccord | disagreement |
| ordre (order) | désordre | disorder, mess |
| avantage (advantage) | désavantage | disadvantage |
| honneur (honor) | déshonneur | dishonor |
| équilibre (balance) | déséquilibre | imbalance |
| espoir (hope) | désespoir | despair |
| obéissance (obedience) | désobéissance | disobedience |
| illusion | désillusion | disillusionment |
| information | désinformation | disinformation |
| intéressé (interested) | désintéressé | disinterested, selfless |
| habillé (dressed) | déshabillé | undressed |
Le bruit du chantier est vraiment désagréable, surtout le matin.
The construction site noise is really unpleasant, especially in the morning.
Ma chambre est en désordre, je vais ranger ce soir.
My room is a mess — I'll tidy up tonight.
Il y a un désaccord profond entre les deux partis.
There's a deep disagreement between the two parties.
Le désespoir l'a poussé à abandonner ses études.
Despair pushed him to give up his studies.
The corresponding adjectives form derived adverbs in -ment: désagréablement (unpleasantly), désespérément (desperately), désordonné/désordonnément (disorderly).
Pronominal dé- verbs
Many dé- verbs have a pronominal (reflexive) form that adds an additional layer of "doing the action to oneself."
Je me déshabille en rentrant, je préfère être en pyjama.
I undress when I get home — I prefer being in pajamas.
Il faut se démaquiller chaque soir, c'est important pour la peau.
You have to take your makeup off every night — it's important for your skin.
Elle s'est décidée à partir, c'est définitif.
She has made up her mind to leave — it's final.
Note the last example: se décider means "to make up one's mind" — a fixed pronominal idiom that has departed somewhat from the literal "undo deciding" reading.
Cases where dé- has lost its reversal meaning
A few dé- verbs no longer carry the reversal sense. Some are old formations where the prefix has fossilized; others have shifted in meaning over time.
| Verb | Looks like reversal of... | Actual meaning |
|---|---|---|
| démontrer | "un-show" (montrer = show) | demonstrate, prove (positive sense — show clearly) |
| décrire | "un-write" (écrire = write) | describe (from Latin describere) |
| déclarer | "un-clear" (clarus = clear) | declare, state publicly |
| découvrir | "un-cover" (couvrir = cover) | discover, uncover (both senses) |
| déjeuner | "un-fast" (jeûner = fast) | have lunch (originally "break fast" — same root as English breakfast) |
| dépenser | "un-think" (penser = think) | spend (money); from Latin dispendere |
Cette étude démontre clairement les effets du changement climatique.
This study clearly demonstrates the effects of climate change.
On déjeune ensemble demain à midi ?
Shall we have lunch together tomorrow at noon?
J'ai dépensé tout mon argent en livres.
I spent all my money on books.
The shared feature: in each, dé- is a fossilized Latin prefix (Latin dis- or de-) and the verb does not mean the negation of the base verb. Démontrer does not mean "un-show"; it means "demonstrate, prove." Learn these as exceptions.
Productivity: when can I make new dé- verbs?
The dé- prefix is moderately productive. Native speakers create new dé- verbs less freely than they create re- verbs, but the system is open.
Reliable patterns:
- Verbs of attachment, fastening, joining → dé- verb of detachment. Coller / décoller, visser / dévisser, attacher / détacher, raccrocher (hang up the phone) / décrocher (pick up the phone).
- Verbs of dressing, putting things on the body → dé- verb of removal. Habiller / déshabiller, chausser / déchausser, maquiller / démaquiller.
- Technical processes that have an inverse operation → modern dé- coinage. Configurer / déconfigurer, installer / désinstaller, bloquer / débloquer, programmer / déprogrammer, zipper / dézipper.
Je vais désinstaller cette application, je ne l'utilise jamais.
I'm going to uninstall this app — I never use it.
Le service technique a finalement réussi à débloquer mon compte.
The technical service finally managed to unblock my account.
Less reliable:
- Stative verbs (aimer, savoir, connaître) generally do not take dé-. There is no désaimer in standard French (though désamour exists as a noun meaning "falling out of love").
- Motion verbs rarely take dé- (use re- for "go back" instead). There is décoller (take off) but not generally démonter au sens d'inverser le mouvement vers le bas.
Source-language note: English vs French
English splits the work of reversal across three prefixes — un-, de-, dis- — that have somewhat different distributions.
- Un- attaches mostly to verbs (untie, undo, unplug) and adjectives (unhappy, unable).
- De- attaches mostly to verbs of Latin origin (defrost, deactivate, demobilize).
- Dis- attaches mostly to abstract nouns and adjectives (disagreement, disorder, disadvantage).
French uses dé- / dés- for all three. This is unusually clean.
The flip side: English makes de- very productive in technical compounds. New verbs are coined on the fly: deauthorize, deprioritize, desync. French is more conservative — it accepts these in technology speech (déprioriser, désynchroniser) but they sound more borrowed than native. Translations of technical English may use dé- freely; native French composition uses it more sparingly.
Common Mistakes
Mistake 1: Forgetting the -s- before a vowel.
❌ Il y a un déaccord entre eux.
Before a vowel, the prefix is dés- (with the -s-): désaccord, not *déaccord.
✅ Il y a un désaccord entre eux.
There's a disagreement between them.
Mistake 2: Adding -s- before a consonant.
❌ Tu peux désbrancher la télé ?
Before a consonant, the prefix is just dé-, not dés-: débrancher, not *désbrancher.
✅ Tu peux débrancher la télé ?
Can you unplug the TV?
Mistake 3: Reading démontrer as "un-show."
❌ J'ai démontré la maison à l'agent immobilier.
Démontrer means 'demonstrate, prove' — not 'un-show.' For 'show a place,' use montrer or faire visiter.
✅ J'ai fait visiter la maison à l'agent immobilier.
I showed the house to the real estate agent.
Mistake 4: Inventing dé- forms that don't exist.
❌ Je vais déaimer ce post sur les réseaux sociaux.
*Déaimer is not French. Use 'ne plus aimer' or 'retirer le j'aime' / 'unliker' (very colloquial).
✅ Je vais retirer mon j'aime de ce post.
I'm going to take back my like on this post.
Mistake 5: Treating décoller as if it only meant "take off" (airplane sense).
❌ J'ai décollé le timbre de l'enveloppe (= I took the stamp off in flight).
Décoller covers both senses — 'unstick' (a stamp, a sticker, a piece of tape) and 'take off' (an airplane, metaphorically a project). Context disambiguates; don't force the airplane reading on every occurrence.
✅ J'ai décollé le timbre de l'enveloppe pour le mettre dans ma collection.
I peeled the stamp off the envelope to add it to my collection.
Mistake 6: Using dé- where French wants a different verb entirely.
❌ Je n'arrive pas à dénouer ce nœud, c'est trop serré.
Possible — but for 'untie shoelaces,' délacer is more idiomatic; for 'untie a knot,' dénouer is correct. Just make sure you pick the verb that matches what you're untying.
✅ Je n'arrive pas à délacer mes chaussures, le nœud est trop serré.
I can't untie my shoes — the knot is too tight.
Key takeaways
- The dé- / dés- prefix expresses reversal, removal, or negation. It corresponds roughly to English un-, de-, and dis- together.
- Spelling: dés- before a vowel or silent h- (désaccord, déshabiller); dé- before a consonant (défaire, démonter).
- Three senses: (1) undo an action (défaire, démonter, décongeler); (2) remove the thing named (dépoussiérer, déboiser); (3) negate a noun or adjective (désaccord, désagréable).
- Fossilized formations (démontrer, décrire, déjeuner, dépenser) no longer carry reversal meaning. Learn them as exceptions.
- The prefix is moderately productive, especially with verbs of attachment, dressing, and technical processes. Modern coinages: désinstaller, débloquer, déprioriser.
- English speakers: where English uses un-, de-, or dis-, French very often uses dé- / dés-. The mapping is one of the most reliable in the language.
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