Les Mots Composés

French has built up an enormous inventory of compound nouns, mostly written with hyphens (porte-monnaie, sous-marin, arc-en-ciel, chef-d'œuvre) and a smaller set written as multi-word phrases without hyphens (pomme de terre, chemin de fer). The compounding patterns and pluralization rules are among the most reliably confusing parts of French orthography — confusing enough that the 1990 spelling reform tried to simplify them.

This page covers the main compounding patterns and the pluralization rule that ties them together. The pluralization looks intimidating but reduces to one principle: only nouns and adjectives can take a plural mark; verbs, prepositions, and adverbs stay invariable in compounds.

The main compounding patterns

Verb + noun

Probably the most distinctive French compound pattern. A bare verb stem (the third-person singular form, which for -er verbs looks identical to the je form) is followed by a noun naming what the verb acts on. The compound is a noun describing a tool, container, or person performing the action. The whole compound is always masculine, regardless of the gender of the embedded noun.

Noun + noun

A noun + noun compound names a thing whose two parts are conceptually linked. The first noun usually carries the gender of the whole.

Noun + de + noun

This pattern uses the preposition de to subordinate one noun to another, naming a thing of a thing. The gender of the compound is that of the first noun.

Note the orthographic distinction: chef-d'œuvre and arc-en-ciel take hyphens because the whole expression is a single lexicalized unit; pomme de terre, chemin de fer, salle de bains do not, because the prepositional phrase still feels syntactically transparent. The distinction is conventional and you should treat each item as a fixed entry.

Adjective + noun and noun + adjective

The adjective can precede or follow the noun, hyphenated for fully lexicalized compounds.

Preposition + noun (and sous-, sur- compounds)

A small but useful pattern: the prepositions sous, sur, avant, après, contre, entre, etc., attached to a noun to form a compound.

Pluralization: the master principle

This is where students often despair. The Académie's rules look like a maze of exceptions. But there is one underlying principle that covers nearly every case:

Only nouns and adjectives can take a plural mark. Verbs, prepositions, and adverbs are invariable in compounds.

Apply this to each component, decide whether semantics also justifies pluralizing it, and you have the answer.

Verb + noun: the verb stays invariable; the noun pluralizes (or not) by meaning

The verb is by definition unchangeable. The noun pluralizes only if it makes semantic sense to do so.

• un porte-monnaie → des porte-monnaie (carries some money — collective, no plural)
• un porte-clés → des porte-clés (already plural)
• un tire-bouchon → des tire-bouchons (each tool pulls a cork — pluralizes)
• un ouvre-boîte → des ouvre-boîtes (each tool opens a can — pluralizes)
• un gratte-ciel → des gratte-ciel (only one sky — invariable)
• un porte-parole → des porte-parole (one collective voice — invariable)

Under 1990 reform spelling, every singular noun pluralizes regularly: des porte-monnaies, des essuie-glaces. The Académie accepts both. Traditional invariable spellings still dominate; reform spellings are gaining ground.

Noun + noun: both pluralize if both are countable

If both nouns are countable and both make sense in the plural, both take -s.

• un wagon-restaurant → des wagons-restaurants
• un bateau-mouche → des bateaux-mouches
• un chou-fleur → des choux-fleurs
• une station-service → des stations-service (service is uncountable here — invariable)
• un timbre-poste → des timbres-poste (poste = postal service, uncountable — invariable)

Noun + de + noun: only the first noun pluralizes

The second noun in a de-construction is fundamentally a modifier and stays invariable in the standard plural.

• une pomme de terre → des pommes de terre
• un chemin de fer → des chemins de fer
• une salle de bains → des salles de bains (bains is already plural in the singular form — frozen)
• un coup d'œil → des coups d'œil
• un chef-d'œuvre → des chefs-d'œuvre
• un arc-en-ciel → des arcs-en-ciel

Adjective + noun: both pluralize

Both the adjective and the noun are inflected. The adjective also agrees in gender with the noun.

• un grand-père → des grands-pères
• une grand-mère → des grands-mères (note: traditional grand invariable; reform allows grandes-mères)
• un coffre-fort → des coffres-forts
• un rouge-gorge → des rouges-gorges

The fixity of grand in grand-mère (no feminine -e) reflects an Old French form where grand was invariable in gender — an archaism the modern spelling preserves.

Preposition + noun: noun pluralizes; preposition stays

The preposition does not inflect. The noun does.

• un sous-marin → des sous-marins
• un avant-bras → des avant-bras (already in -s, invariable)
• un après-midi → des après-midi (invariable by tradition; reform allows après-midis)

Gender of compound nouns

• Verb + noun compounds are always masculine — un porte-monnaie, un tire-bouchon, un gratte-ciel — regardless of the embedded noun's gender.
• Noun + noun and noun + de
  • noun
  compounds inherit the gender of the first noun: une pomme de terre, un chemin de fer, un wagon-restaurant.
• Adjective + noun compounds inherit the noun's gender: un grand-père, une grand-mère, un coffre-fort, une basse-cour.

The 1990 spelling reform

The 1990 reform proposed two changes: standardize pluralization (every singular noun pluralizes regularly — des porte-monnaies) and remove hyphens from some compounds, fusing them into single words (portemonnaie, piquenique, weekend). Both spellings are now accepted. Older publishers stay with pre-reform forms; newer textbooks use reform forms. Pick one and stay consistent.

Source-language note: English compounds vs French compounds

English builds compounds by simple juxtaposition (bookshelf, toothpick, can opener); French uses hyphens or de-phrases (cure-dent, ouvre-boîte, sèche-cheveux). Three differences matter:

• French compounds are typically left-headed. Wagon-restaurant is a wagon (kind: restaurant). English is right-headed: dining car is a car. This is why the first noun in French determines the gender.
• English compounds rarely use prepositions internally. Cuckoo clock, not "clock of cuckoo." French reaches for de: salle de bains, coup de foudre, queue de cheval.
• French verb + noun compounds have no real English parallel. English says can opener (gerund + noun); French says ouvre-boîte (bare verb + noun). The French verb is finite, not a participle.

Common Mistakes

Mistake 1: Wrong word order in verb + noun compounds.

Mistake 2: Pluralizing the verb in a verb + noun compound.

Mistake 3: Pluralizing the second noun in a noun + de + noun compound.

Mistake 4: Making a verb + noun compound feminine because the embedded noun is feminine.

Mistake 5: Forgetting to hyphenate a lexicalized compound.

Mistake 6: Mixing pre-reform and reform spellings within the same text.

Key takeaways

• French builds compounds in two main ways: hyphenated (most common — porte-monnaie, grand-père, arc-en-ciel) and non-hyphenated phrases (a smaller set — pomme de terre, chemin de fer).
• The main patterns are: verb + noun (tire-bouchon), noun + noun (wagon-restaurant), noun + de
  • noun (chef-d'œuvre), adjective + noun (grand-père), preposition + noun (sous-marin).
• Gender: verb + noun compounds are always masculine; other compounds inherit the gender of the (first or head) noun.
• Pluralization reduces to one principle: only nouns and adjectives can take a plural mark; verbs, prepositions, and adverbs stay invariable. Apply to each component; pluralize only if semantically justified.
• The 1990 spelling reform simplified some plural rules and removed some hyphens, but pre-reform spellings remain common. Pick a system and stay consistent.
• French verb + noun compounds (sèche-cheveux, ouvre-boîte) have no direct English parallel. The verb comes first, the object second. Word order is fixed.