Cher vs. coûteux
In French, the words cher and coûteux both translate into English as expensive, but they are used in different contexts and have slightly different connotations.
Cher
A2The word cher is widely used in everyday French. It can be used to describe things of high price, but it also carries a sense of value, affection, or emotional worth. It is often used in a broader range of contexts than coûteux.
Cette montre est très chère.
(This watch is very expensive.)
Je tiens à ces moments, ils me sont très chers.
(I cherish these moments; they are very dear to me.)
Coûteux
B1The word coûteux strictly refers to a high monetary cost. It lacks the emotional connotation and is typically used in formal situations or to emphasize the high cost from an economic point of view.
Le projet s'est avéré plus coûteux que prévu.
(The project turned out to be more costly than expected.)
Les réparations vont être coûteuses.
(The repairs are going to be expensive.)
Summary
Cher and coûteux both mean expensive, but cher can express emotional value and is more widely used, while coûteux focuses on the financial aspect and is generally more formal.