Vocabulary in The Necklace
While contextually readers will correctly understand that "paste" in this context means a "fake," this is based on one of the additional meanings of the word "paste." When used as a noun, "paste" can refer to a heavy, clear-flint glass that is used for making imitation gems, such as diamonds.
Compared to a louis or a franc, the sou is the least valuable form of currency from 19th-century France. This means that she has become extremely aware of the value and amount of money she has, and she does not want to spend anything unnecessarily.
Garrets are small rooms in the roof of a building. Due to their being small, and typically dingy, they were the cheapest rooms to rent and served as homes for many of the poor.
The deep embarrassment they feel at having failed provides insight into their rationale for not admitting that the necklace was lost in the first place. Despite the friendship that Mathilde has with Madame Forestier, it appears that social obligations and class divisions run so deep in society that they would rather make themselves sick trying to solve the problem instead of admitting their mistake.
An "attaché" is someone who serves on the staff of someone else, an establishment, or an organization. The "Cabinet" here refers to part of the governing political body in Paris. These details serve to remind readers that Mathilde is participating in a high-end, aristocratic ball.
The original French here can also be translated as, "her heart beat covetously." The notion is that her "immoderate desire" represents greed and her belief that she should live like her friend Madame Forestier.
This word choice is important because "fled" means to run away from a place of peril or danger. This gives the impression that Mathilde is afraid her friend might change her mind.
Satin is a smooth, silky material that is fairly expensive and objects made of this material generally give the impression of luxury. Fine pieces of jewelry are often contained in such boxes to protect the craftsmanship.
While an exact conversion to dollars or euros is difficult to make, Mathilde's husband's reaction reveals that this is still a relatively large amount of money. Despite his growing "a little pale," we can see that Monsieur Loisel is willing to put aside his own desires for the sake of his wife's.
The choice of economical here characterizes Monsieur Loisel in two ways. First, it has a positive connotation that suggests he is efficient with spending money and good at his job. This contrasts with the second connotation (which Mathilde likely intends) that negatively characterizes him as cheap and unwilling to spend any money.
This is shorthand for a convent school. Many schools like these were attached to a convent and run by the nuns who lived there. The student population typically consisted of primarily girls. Since she knows her rich friend from school, it is possible that Mathilde's friend acquired her wealth and status through marriage.
Mathilde is not only imagining the objects that she would like to possess, but she is also considering the social interactions and behaviors she wishes were a part of her life. Sphinxlike refers to something that is mysterious or difficult to understand. In her mind, only these kinds of inscrutable smiles are appropriate for upper-class persons.
When Maupassant was writing, the term "oriental" was used to refer to any culture, region, or state located to the physical east of Europe, the Mediterranean, and generally the Christian world of the time. Methilde uses it simply to refer to her desire for exotic and expensive possessions.