A compound noun brings together two or more words to designate a single reality. It functions as a single noun in the sentence. You can encounter very short groups, such as passeport, and more visible groups, such as porte-monnaie or chef-d’œuvre. In all cases, the whole serves to name a person, an object, a place, or an idea, as do the Noms Communs and the Noms propres.

Forming a Simple Lexical Compound

Idea
A compound noun is formed by joining two or more words to create a single idea.
The compound may stay joined even if its elements keep their own meanings.
The compound is read as a single noun in the sentence.
The meaning of the compound is often better understood with the whole than with each word alone.

The most common forms follow a few stable patterns. You find nom + nom in chaussettes-lavette or timbre-poste, nom + préposition + nom in chef d’orchestre, adjectif + nom in bas-bleu, and verbe + nom in porte-clés or garde-fou. These patterns help recognize a compound even when the words keep their basic form. The whole group is read as a single noun, as with the Noms Composés in general.

Nom à nomVerbe nomAdjectif nomNom préposition nomNom sur nomNom verbeNom nomNom de nom

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Ce schéma utilise la préposition à pour relier les éléments du composéCe schéma associe un adjectif à un nom pour créer un bloc lexicalCe schéma relie deux noms avec une préposition pour préciser la relationCe schéma emploie la préposition sur pour marquer un rapport plus rare ou figuréCe schéma réunit deux noms pour former un ensemble lexicalCe schéma utilise la préposition de pour préciser une relation ou une matièreCe schéma combine une forme verbale et un nom pour nommer un objet ou une action figéeCe schéma place un nom avant une forme verbale dans un composé lexical

Common Schemes of Compound Nouns

Word	Definition
Nom nom	This scheme brings two nouns together to form a lexical unit.
Nom préposition nom	This scheme links two nouns with a preposition to specify the relation.
Adjectif nom	This scheme attaches an adjective to a noun to create a lexical block.
Verbe nom	This scheme combines a verb form and a noun to name a fixed object or action.
Nom verbe	This scheme places a noun before a verbal form in a lexical compound.
Nom à nom	This scheme uses the preposition à to link the elements of the compound.
Nom de nom	This scheme uses the preposition de to specify a relation or a material.
Nom sur nom	This scheme uses the preposition sur to mark a rarer or figurative relation.

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The meaning of a compound noun is not always deduced word by word. Un gratte-ciel does not mean a sky that one scratches, and un rouge-gorge does not merely describe the color of the throat. The compound often takes on a full lexical meaning, fixed by usage. It is therefore necessary to learn the overall value of the group, just as one learns the meaning of an isolated noun. This behavior makes the compound resemble a block of single meaning, useful to know with the Noms collectifs when the whole designates a global reality.

Interpreting the Lexical Global Meaning

Usage	Explanation
Fixed meaning	We learn the meaning of the entire compound because it is not always deducible word-for-word.
Lexical block reading	We sometimes treat the compound as a single unit of meaning even if several words appear.
Figurative meaning	We keep an eye on the figurative meaning when the compound sounds funny or surprising.
Specialized meaning	We retain the technical meaning when the compound belongs to a specific field.
Unexpected meaning	We accept the gap between the words and the final meaning when the compound is surprising.

The gender of a compound noun is often determined by the main word, the one that bears the central meaning. In une porte-fenêtre, the main word is porte, so the noun is feminine. In un chef-d’œuvre, the main word is chef, so the noun is masculine. When the compound is fixed, its gender is memorized with the whole, especially if the word order does not make the main meaning clearly appear. This principle complements the Genre nominal and also applies to fixed lexical forms.

Determining the Gender of the Compound

Idea
Gender is often carried by the head word of the compound.
When the compound refers to a person, the gender may follow the referent's sense.
Some compounds keep a fixed gender learned as a whole.
Gender may seem surprising when the head of the compound is less visible.

The plural of a compound noun depends on its structure. Some elements take the plural marker, others stay invariable, and some compounds pluralize as a single noun. We write des porte-monnaie because the first element often keeps the singular form when the compound denotes a single fixed-type object. We write des coffres-forts when each part follows the group’s logic. The global meaning also matters: if the compound denotes a single class of objects, the form may remain stable. The nominal number thus does not always show on every word, which directly links these forms to the Nombre nominal.

Forming the Plural of Compounds

Idea
We often place the head noun in the plural when the compound follows the logic of a simple noun.
Invariable elements stay in the singular when they do not inflect.
Some compounds keep a fixed plural according to traditional use.
The overall sense sometimes guides a particular plural that does not follow word-for-word.
When the compound designates a single object, the plural does not change all in the frozen expression.

The determiner agrees with the entire compound noun, as with a simple noun. We say le chef-d’œuvre, la porte-fenêtre, les chefs-d’œuvre, les portes-fenêtres. The article does not agree with each word of the compound separately; it accompanies the nominal whole. When the compound is preceded by a possessive or a demonstrative, the form chosen always depends on the compound noun as a whole: ce porte-clés, mon garde-fou, ces timbres-poste. The behavior of the determiner thus follows the general rules of Noms while applying to a complex lexical unit.

Agreeing the determiners of the compound

Usage	Explanation
Definite determiner	We accord the definite article with the whole compound noun as with a simple noun.
Indefinite determiner	We choose a natural determiner for the gender and number of the compound.
Demonstrative determiner	We accord this determiner with the whole compound, not with a single isolated word.
Possessive determiner	We put the possessive in the correct gender and number of the entire compound.

The hyphen often appears in compound nouns, especially when the form is tightly joined: passe-temps, grand-mère, arc-en-ciel. Other compounds are written with a space, like chef d’orchestre, and some forms remain fixed by tradition, with a spelling that must be remembered as is. The absence or presence of the hyphen depends therefore on the established usage of the word. When the compound is well established in the language, its spelling is part of its identity, just as its gender and its plural.

usage soupleforme figéetrait d union fréquentorthographe traditionnelle

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On conserve parfois une orthographe héritée qui reste très stable dans les textes formelsOn rencontre souvent le trait d union dans beaucoup de composés, surtout dans l usage traditionnelOn trouve parfois une écriture plus souple selon les ouvrages et les habitudes éditorialesCertaines expressions restent figées par l usage même si la ponctuation varie peu

Orthographic Uses of Compounds

Region	Variant	Definition	Example
France	trait d union fréquent	The hyphen is commonly found in many compounds, especially in traditional usage.	Le porte monnaie et le porte clés apparaissent souvent avec un trait d union dans les écrits soignés.The porte monnaie and the porte clés often appear with a hyphen in carefully written texts.
Belgium	orthographe traditionnelle	Sometimes we keep an inherited spelling that remains very stable in formal texts.	La machine à écrire garde sa forme classique.The machine à écrire keeps its classic form.
Switzerland	forme figée	Some expressions stay frozen by usage even if punctuation varies little.	Le gratte ciel garde son allure de géant urbain.The gratte ciel keeps its urban giant look.
Canada	usage souple	Sometimes we find a more flexible spelling depending on works and editorial habits.	Le pomme de terre du marché semblait très célèbre dans la légende du déjeuner.The pomme de terre from the market seemed very famous in the legend of the lunch.

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