Demimonde was a polite 19th century term that was often used the same way we use the term “mistress” today. In the 19th century it primarily referred to a class of women on the fringes of respectable society supported by wealthy lovers (usually each had several). The term is also used to refer to these women as a group, and the social circles they moved in. As a group, the demimonde did not form a ‘society’ any more than modern prostitutes form a society. But they did represent a social class of women in the latter half of the 19th century and into the early 20th century who were commonplace fixtures in the upper class of French, English and, to some extent, American society. In the United States and Britain, they were (and still are) also often referred to as courtesans, though that term in the 19th century applied to a profession (as the term “prostitute” describes a profession), whereas Demimonde/Demimondaine was used to describe a broader social class. The term is French, and means literally “half-world”, implying those women existed on the fringes of the “real world.” It derives from a comedy by Alexandre Dumas fils published in 1855 called Le Demi-Monde.
Descriptions of the demimonde can be found in Vanity Fair, a novel which satirizes 19th century society written by William Makepeace Thackeray. Although it does not mention the terms ‘demimonde’ and ‘demimondaine’ (they were coined later), the terms were later used by reviewers and other authors in reference to three characters in it.