Many English adjectives ending in -ous have close French matches ending in -eux. This is one of the most useful word patterns in French. It can help with reading and guessing meaning, because a large number of English and French words come from the same Latin roots.

Examples such as dangerous → dangereux and curious → curieux show the pattern well.

This pattern is often reliable, but it is not a rule that always works. Some words follow other paths, and some have shifted in meaning over time.

The basic pattern

The usual pattern is:

• English -ous → French -eux
• English -ous → French -euse for feminine forms

Examples:

• dangerous → dangereux
• curious → curieux
• nervous → nerveux
• generous → généreux
• mysterious → mystérieux
• serious → sérieux
• ambitious → ambitieux
• courageous → courageux

Examples with feminine forms:

• dangerous → dangereuse
• curious → curieuse
• generous → généreuse

Examples:

• Un homme dangereux. “A dangerous man.”
• Une femme dangereuse. “A dangerous woman.”
• Un enfant curieux. “A curious child.”
• Une fille curieuse. “A curious girl.”

Common examples

Dangerous → dangereux

Examples:

• Ce chien semble dangereux. “That dog seems dangerous.”
• Cette route est dangereuse. “This road is dangerous.”

Related words:

• danger “danger”
• mettre en danger “to put at risk”

Curious → curieux

Examples:

• Il est très curieux. “He is very curious.”
• Je trouve cela curieux. “I find that strange.”

French curieux can also mean strange or odd.

Examples:

• C’est une curieuse histoire. “That is a strange story.”

Related words:

• curiosité “curiosity”

Nervous → nerveux

Examples:

• Il devient nerveux avant les examens. “He becomes nervous before exams.”
• Elle paraît nerveuse aujourd’hui. “She seems nervous today.”

Related words:

• les nerfs “nerves”

Generous → généreux

Examples:

• Il est très généreux avec ses amis. “He is very generous with his friends.”
• Elle a fait un geste généreux. “She made a generous gesture.”

Related words:

• générosité “generosity”

Mysterious → mystérieux

Examples:

• Il y a un bruit mystérieux dans la maison. “There is a mysterious sound in the house.”
• Elle a un sourire mystérieux. “She has a mysterious smile.”

Related words:

• mystère “mystery”

Cases where spelling changes more

Some words follow the pattern, but other parts of the word change as well.

Examples:

• ambitious → ambitieux
• cautious → prudent
• furious → furieux
• precious → précieux
• religious → religieux

The ending may still fit the pattern, but the whole word may not line up exactly.

Examples:

• Il est très ambitieux. “He is very ambitious.”
• Cette bague est précieuse. “This ring is precious.”
• Il est furieux contre son voisin. “He is furious with his neighbour.”

Related words:

• ambition “ambition”
• furie “fury”
• prix “price”

Cases where the pattern fails

Not every English -ous word becomes French -eux.

Examples:

• famous → célèbre
• jealous → jaloux
• enormous → énorme
• poisonous → toxique
• glamorous → glamour

Examples:

• Il est célèbre dans son pays. “He is famous in his country.”
• Elle est jalouse de sa sœur. “She is jealous of her sister.”
• Cet animal est toxique. “This animal is poisonous.”

You cannot safely change every English -ous word into -eux.

Watch out for false friends

Some words look closely linked but have grown apart.

Curious → curieux

As already seen, curieux can mean more than curious.

Examples:

• Je trouve cela curieux. “I find that strange.”
• Un curieux personnage est arrivé. “A strange person arrived.”

English curious usually stays closer to the idea of wanting to know things.

Serious → sérieux

French sérieux can mean serious, but also reliable or solid.

Examples:

• Cette entreprise semble sérieuse. “This company seems reliable.”
• Il faut être sérieux. “You must be serious.”

Larger word families

Many of these words belong to larger groups.

English noun	English adjective	French noun	French adjective
danger	dangerous	danger	dangereux
mystery	mysterious	mystère	mystérieux
courage	courageous	courage	courageux
nerve	nervous	nerf	nerveux
generosity	generous	générosité	généreux

Learning families often helps more than learning single words.

Useful examples in full sentences

• Le brouillard rend la route dangereuse. “The fog makes the road dangerous.”
• Mon fils est très curieux de nature. “My son is naturally very curious.”
• Elle devient nerveuse avant une réunion. “She becomes nervous before a meeting.”
• Cet homme est très généreux avec son temps. “That man is very generous with his time.”
• Il y a quelque chose de mystérieux dans cette maison. “There is something mysterious about this house.”
• Son frère est ambitieux depuis son enfance. “His brother has been ambitious since childhood.”

Related patterns

The English -ous → French -eux pattern belongs to a wider set of useful links.

Examples:

• English -ty → French -té
• English -ncy → French -nce
• English -ity → French -ité

Examples:

• liberty → liberté
• frequency → fréquence
• activity → activité

These links help with guessing meaning, but they should be treated as guides rather than fixed rules.

Summary

• English adjectives ending in -ous often match French adjectives ending in -eux.
• Feminine forms usually end in -euse.
• Many pairs come from shared Latin roots.
• Common examples include dangerous → dangereux and curious → curieux.
• Some words fail to follow the pattern, such as famous → célèbre.
• Learning whole word families often works better than learning isolated words.