Les Noms Composés

A compound noun in French is a noun built from two or more elements joined together — usually with a hyphen, sometimes with a space, occasionally fused into a single word. Examples include un arc-en-ciel (a rainbow), un porte-monnaie (a coin purse), un grand-père (a grandfather), un chou-fleur (a cauliflower), un sous-marin (a submarine), un savoir-faire (a know-how). The challenge is not learning what they mean — most are transparent from their parts — but learning how to pluralize them. This is one of the most notorious difficulties in French grammar, and one of the only areas where native speakers themselves consult dictionaries.

The good news: there is a system. The plural depends on the parts of speech that make up the compound, and once you can analyse the structure (verb + noun? noun + noun? noun + preposition + noun?), the rule follows. This page walks through the six main structural patterns, gives extensive lists of common compounds for each, and ends with a survey of the irregular cases that defy the system. By the end, you should be able to predict the plural of an unfamiliar compound about 85% of the time — and know which 15% to look up.

The general principle

In French compound nouns, the plural -s is added to whichever element is inflectable (a noun or an adjective) and logically pluralizable in context. Verbs, adverbs, and prepositions never take a plural marker because they are not nouns; they are invariable.

This single principle generates all six patterns below. Once you know which elements are nouns/adjectives (capable of taking -s) versus verbs/prepositions/adverbs (always invariable), the rule writes itself.

Pattern 1: Noun + Noun — both pluralize

When a compound is made of two nouns, both nouns take a plural -s (or -x where appropriate).

Note the spelling oddity in gentilhomme / gentilshommes and bonhomme / bonshommes: the -s lands inside the compound rather than at the end. These are historical relics from when the elements were felt as separable.

Pattern 2: Noun + Adjective (or Adjective + Noun) — both pluralize

When a compound consists of a noun and a qualifying adjective, both elements pluralize because both are inflectable. The adjective also agrees in gender with the noun.

A subtlety: grand-mère is sometimes written grand'mère in older texts, and the grand historically did not agree in the feminine — which is why you still see des grand-mères alongside des grands-mères. The 1990 spelling reform regularized agreement, so modern usage is grands-mères. Both forms are accepted.

Pattern 3: Verb + Noun — only the noun pluralizes

This is the pattern that catches learners most often. When a compound starts with a verb (typically a third-person singular present indicative form) followed by a noun, the verb is invariable — verbs cannot take plural marks. Only the noun pluralizes, and only if the noun is itself logically pluralizable.

The key insight is that porte in porte-monnaie, porte-clés, porte-bagages is the verb porter — the thing that carries — not the noun la porte (door). Once you see this, porte-monnaie parses as carries-money, and the porte part stays invariable in the plural.

Special case: porte-monnaie — invariable

Un porte-monnaie is fascinating because monnaie (change, currency) doesn't really have a plural in this context — you carry currency, not currencies, in a coin purse. So traditional usage keeps the whole compound invariable: des porte-monnaie. The 1990 reform allows des porte-monnaies, but most writers still prefer the invariable form. Both are accepted.

For exam purposes, write whichever form your textbook teaches; both are correct in modern French.

Pattern 4: Noun + Preposition + Noun — only the first noun pluralizes

When a compound consists of Noun + Preposition + Noun, only the first noun takes the plural mark. The preposition is invariable, and the second noun's role is to specify or modify, not to pluralize.

( *Une pomme de terre, feminine. Listed here for the pluralization. *timbre-poste is etymologically *timbre de poste; the de has dropped from the surface form but the structure persists.)

The reasoning: un arc-en-ciel is an arc in the sky. There can be many arcs but only one sky, so only arc pluralizes. The same logic governs chef-d'œuvre (masterpiece), pot-au-feu (one fire, many pots), and hôtel-Dieu (one God, many hospitals).

Pattern 5: Adverb + Noun — only the noun pluralizes

Adverbs are invariable. When an adverb (often avant, arrière, bien, mal) precedes a noun in a compound, only the noun pluralizes.

A subtle case: haut is sometimes felt as an adjective (haut meaning high), but in haut-parleur it functions adverbially (loud-speaker, the speaker that speaks loudly). The compound is treated as adverb + noun, so only parleur pluralizes.

Pattern 6: Sub-words from foreign or fixed sources — invariable

A small set of compounds — typically borrowings, Latin phrases, or fossilized expressions — stays invariable in the plural. The compound is treated as a single unit, and -s is not added at all.

These compounds resist analysis: savoir-faire is verb + verb (no noun to pluralize); va-et-vient is verb + conjunction + verb (no noun at all); hors-d'œuvre contains a preposition where the head normally is. With nothing inflectable, the form stays put.

Sous-marin, sous-titre — prefix + noun

A productive class with the prefix sous- (under-) or sur- (over-): the prefix is invariable, the noun pluralizes.

These behave like ordinary nouns once you accept sous- and sur- as fixed prefixes.

Quick decision flowchart

When you face an unfamiliar compound and need to pluralize it:

1. What's the structure? Identify each element's part of speech.
2. Is the first element a verb? If yes, it stays invariable. Pluralize the noun if it's logically pluralizable.
3. Is the first element an adverb or invariable preposition? If yes, it stays invariable. Pluralize the noun.
4. Are both elements nouns or noun + adjective? Both pluralize.
5. Is the structure Noun + Preposition + Noun? Only the first noun pluralizes.
6. Is the compound a fixed expression with no clear noun head (like savoir-faire, hors-d'œuvre)? Probably invariable; check a dictionary.
7. Is the second noun something there is normally only one of (ciel, Dieu, terre as 'earth')? It probably stays singular.

A note on the 1990 reform

The 1990 spelling reform proposed simplifying compound-noun pluralization by treating compounds as single words and pluralizing only the final element (so des porte-monnaies, des arc-en-ciels). The reform is officially endorsed but in practice optional; most published writing, traditional dictionaries, and the Académie française still follow the patterns above. Schools teach both. For learners, the safer choice is the traditional rule, which is universally recognized.

Common Mistakes

This is the most common mistake. Porte in porte-monnaie is the verb carries, not the noun door; verbs don't take plural marks.

Both elements of grand-père are inflectable: grand is an adjective, père is a noun. Modern French agrees both.

In Noun + Preposition + Noun compounds, only the first noun pluralizes. The second noun (ciel) stays in its original form.

Both chou and fleur are nouns and both inflect for plural.

Compounds built on verbs stay invariable when there's nothing inflectable to mark.

The expression contains a preposition (hors) and a noun governed by de; with no inflectable head accessible, the form is invariable.

There is only one ciel (sky); the noun stays singular even when the compound itself is plural. Many gratte-ciel scrape one sky.

Key Takeaways

The pluralization of French compound nouns follows the part-of-speech rule: only nouns and adjectives can take plural marks; verbs, prepositions, and adverbs are invariable. Apply this principle consistently and the six patterns fall into place. Verb + noun pluralizes only the noun. Noun + noun pluralizes both. Noun + adjective pluralizes both, with adjective agreement. Noun + preposition + noun pluralizes only the first noun. Adverb + noun pluralizes only the noun. Fixed verb-verb or hors-system compounds stay invariable. When in doubt, parse the compound carefully — and for a small set of edge cases (porte-monnaie, abat-jour, the 1990 reform), accept that both forms exist and pick the one your audience expects.