How do you make a French compound noun plural?

Split it at the hyphen and pluralise only the nouns and adjectives inside it. Un coffre-fort gives des coffres-forts because both halves qualify, while un ouvre-boîte gives des ouvre-boîtes because ouvre is a verb and cannot take an ending.

Why is it des gratte-ciel with no -s?

Because the compound means something that scrapes the sky, and there is only one sky to scrape. Gratte is a verb, so it is frozen, and ciel stays singular for reasons of meaning. The 1990 reform permits des gratte-ciels, but the older form is still the usual one.

Which part of arc-en-ciel takes the plural?

The first: des arcs-en-ciel. The same happens with des chefs-d'œuvre and des pommes de terre, where the second noun belongs to a prepositional phrase describing the first and therefore never changes.

Do compound nouns written as one word follow the same rules?

No. Once a compound is written solid, French treats it as a plain noun and adds -s to the end: des portefeuilles, des pourboires, des passeports. The exceptions are monsieur, madame, mademoiselle, bonhomme and gentilhomme, which still pluralise both halves.

What changed with the 1990 spelling reform?

It allowed verb + noun and preposition + noun compounds to behave predictably: singular in the singular, plural in the plural. That gives des après-midis and des porte-monnaies alongside the traditional des après-midi and des porte-monnaie. Both are accepted.

French grammar · Advanced

French Compound Noun Plurals: Which Half Takes the -s

Written by Camille Laurent, Lead French Curriculum Editor · Reviewed May 2026

A French compound noun pluralises from the inside out: only the nouns and adjectives within it can take a plural mark, and verbs, prepositions and adverbs never do. That is why un chou-fleur gives des choux-fleurs but un ouvre-boîte gives des ouvre-boîtes, with the verb ouvre untouched.

Nous avons acheté deux choux-fleurs et trois tire-bouchons.

We bought two cauliflowers and three corkscrews.

What it is

A compound noun is two or more words hyphenated into one meaning, and French pluralises it by looking at each part separately and asking what part of speech it is. Nouns and adjectives can carry a plural; verbs, prepositions and adverbs cannot. Once you have identified the parts, the answer usually falls out on its own.

un coffre-fort → des coffres-forts, un gratte-ciel → des gratte-ciel — a safe → safes, a skyscraper → skyscrapers.

How to spot it

Break the compound at the hyphen and label each half. If a half is a verb form like porte, ouvre, essuie, gratte or tire, it will not move whatever happens.

un chou-fleur → des choux-fleurs — a cauliflower → cauliflowers (noun + noun)
une belle-mère → des belles-mères — a mother-in-law → mothers-in-law (adjective + noun)
un essuie-glace → des essuie-glaces — a windscreen wiper → wipers (verb + noun)
un arc-en-ciel → des arcs-en-ciel — a rainbow → rainbows (noun + preposition + noun)

The hyphen is not always there. Compounds written as a single word, such as portefeuille and pourboire, behave like any ordinary noun and simply add -s.

Compound Noun Plurals Quick Reference

What pluralises in each type of compound

Structure	What takes the -s	Example
noun + noun	both	un chou-fleur → des choux-fleurs
noun + adjective	both	un coffre-fort → des coffres-forts
adjective + noun	both	une belle-mère → des belles-mères
verb + noun	the noun only, if the sense allows	un tire-bouchon → des tire-bouchons
verb + noun (uncountable)	nothing	un gratte-ciel → des gratte-ciel
noun + preposition + noun	the first noun only	un arc-en-ciel → des arcs-en-ciel
adverb or preposition + noun	the noun only	un haut-parleur → des haut-parleurs
written as one word	the whole word	un portefeuille → des portefeuilles

Common Compound Noun Plurals Examples in French

Each structure with the compounds you are most likely to need:

Noun + Noun: Both Halves Move

un chou-fleur → des choux-fleurs: a cauliflower → cauliflowers
un wagon-lit → des wagons-lits: a sleeping car → sleeping cars
un oiseau-mouche → des oiseaux-mouches: a hummingbird → hummingbirds
un chef-lieu → des chefs-lieux: a county town → county towns

Each half keeps its own plural pattern, so chou takes -x and lieu takes -x while lit takes -s.

Noun + Adjective: Both Halves Agree

un coffre-fort → des coffres-forts: a safe → safes
une basse-cour → des basses-cours: a farmyard → farmyards
un rouge-gorge → des rouges-gorges: a robin → robins
un grand-père → des grands-pères: a grandfather → grandfathers
un sourd-muet → des sourds-muets: a deaf-mute → deaf-mutes

The adjective agrees with the noun beside it exactly as it would in an ordinary phrase, in gender as well as number.

Verb + Noun: Only the Noun Can Move

un tire-bouchon → des tire-bouchons: a corkscrew → corkscrews
un ouvre-boîte → des ouvre-boîtes: a tin opener → tin openers
un essuie-glace → des essuie-glaces: a windscreen wiper → windscreen wipers
un porte-clés → des porte-clés: a keyring → keyrings

Porte-clés already carries its -s in the singular, because a keyring holds keys in the plural even when there is one of them.

Noun + Preposition + Noun: Only the First

un arc-en-ciel → des arcs-en-ciel: a rainbow → rainbows
un chef-d'œuvre → des chefs-d'œuvre: a masterpiece → masterpieces
une pomme de terre → des pommes de terre: a potato → potatoes
un timbre-poste → des timbres-poste: a postage stamp → postage stamps

Timbre-poste is short for timbre pour la poste, so poste stays singular even though the hyphen makes it look like a noun + noun compound.

How Compound Plurals Are Decided

Two questions settle nearly every case: what part of speech is each half, and does the meaning allow a plural at all.

Only Nouns and Adjectives Can Carry a Plural

A plural -s is a mark of number, and only words that have number can wear it. Verbs, prepositions and adverbs have none, so they are frozen inside the compound no matter how many objects you are talking about.

des ouvre-boîtes, des sans-abri

tin openers, homeless people

Verbs and prepositions never move.

Then Ask Whether the Meaning Allows a Plural

Even a noun stays singular if the sense of the compound forbids anything else. A gratte-ciel scrapes the sky, and there is only one sky; a porte-monnaie carries money, which has no plural in that sense.

des gratte-ciel, des porte-monnaie

skyscrapers, purses

One sky, one -ciel.

Each Half Keeps Its Own Plural Ending

When both halves do pluralise, they do it by their own rules rather than copying each other. Chou takes -x, cheval would take -aux, and a noun already ending in -s or -x stays as it is.

des choux-fleurs et des chefs-lieux

cauliflowers and county towns

Two words, two plural rules.

A Preposition Blocks the Second Noun

In arc-en-ciel, pomme de terre and chef-d'œuvre, the second noun sits inside a prepositional phrase that describes the first one. Phrases like that do not pluralise, so only the head noun moves.

des pommes de terre nouvelles

new potatoes

Head noun only.

One-Word Compounds Are Ordinary Nouns

Once a compound has been written solid, French forgets its internal structure and pluralises the whole thing. The only survivors of the old system are the monsieur family, which still pluralises both halves.

des portefeuilles, mais des messieurs

wallets, but gentlemen

Solid word, single -s.

Common Mistakes with Compound Noun Plurals

Incorrect: des chou-fleurs — cauliflowers

Correct: des choux-fleurs — cauliflowers

Both halves are nouns, so both take a plural. Chou is one of the seven -ou nouns that take -x rather than -s, which makes this compound doubly easy to get wrong.

Incorrect: des ouvres-boîtes — tin openers

Correct: des ouvre-boîtes — tin openers

Ouvre is a verb form, and verbs have no number to mark. Only boîte can pluralise, because that is the noun.

Incorrect: des arc-en-ciels — rainbows

Correct: des arcs-en-ciel — rainbows

The plural goes on the head noun, arc. Ciel sits inside a prepositional phrase describing it, and there is only one sky in any case.

Incorrect: des timbre-postes — postage stamps

Correct: des timbres-poste — postage stamps

Timbre-poste is an abbreviation of timbre pour la poste. The head noun timbre pluralises; poste is the remains of a phrase and cannot.

Compounds That Sit Outside the Rules

Three groups you cannot work out from the parts: the fully invariable compounds, the old solid words, and the forms the 1990 reform changed.

Fully invariable compounds

When neither half is a noun that can be counted, nothing at all changes. The article is the only visible plural.

des hors-d'œuvre: starters
des réveille-matin: alarm clocks
des sans-abri: homeless people
des va-et-vient: comings and goings

Des laissez-passer, des on-dit and des sauve-qui-peut belong to the same group. If you cannot find a countable noun inside, expect no ending.

Old solid compounds that still split

A few words written as one piece are historically two, and they pluralise both halves. There are five of them in ordinary use.

monsieur → messieurs: sir → gentlemen
madame → mesdames: madam → ladies
mademoiselle → mesdemoiselles: miss → young ladies
un bonhomme → des bonshommes: a fellow → fellows
un gentilhomme → des gentilshommes: a nobleman → noblemen

Mon, ma and mes are hiding at the front of the first three: messieurs is literally mes sieurs.

What the 1990 spelling reform allows

The reform simplified verb + noun and preposition + noun compounds: the second element is now singular in the singular and plural in the plural, whatever the meaning suggests.

un porte-monnaie → des porte-monnaies: a purse → purses (reformed spelling)
un après-midi → des après-midis: an afternoon → afternoons (reformed spelling)
un gratte-ciel → des gratte-ciels: a skyscraper → skyscrapers (reformed spelling)

Both spellings are correct. Traditional forms remain far more common in print, so recognise the reformed ones rather than adopting them.

Compound Noun Plurals FAQs

How do you make a French compound noun plural?: Split it at the hyphen and pluralise only the nouns and adjectives inside it. Un coffre-fort gives des coffres-forts because both halves qualify, while un ouvre-boîte gives des ouvre-boîtes because ouvre is a verb and cannot take an ending.
Why is it des gratte-ciel with no -s?: Because the compound means something that scrapes the sky, and there is only one sky to scrape. Gratte is a verb, so it is frozen, and ciel stays singular for reasons of meaning. The 1990 reform permits des gratte-ciels, but the older form is still the usual one.
Which part of arc-en-ciel takes the plural?: The first: des arcs-en-ciel. The same happens with des chefs-d'œuvre and des pommes de terre, where the second noun belongs to a prepositional phrase describing the first and therefore never changes.
Do compound nouns written as one word follow the same rules?: No. Once a compound is written solid, French treats it as a plain noun and adds -s to the end: des portefeuilles, des pourboires, des passeports. The exceptions are monsieur, madame, mademoiselle, bonhomme and gentilhomme, which still pluralise both halves.
What changed with the 1990 spelling reform?: It allowed verb + noun and preposition + noun compounds to behave predictably: singular in the singular, plural in the plural. That gives des après-midis and des porte-monnaies alongside the traditional des après-midi and des porte-monnaie. Both are accepted.