The noun cache-sexe designates:
– literally: a small cloth or band worn, as by an otherwise nude dancer, to conceal the genitals;
– figuratively: something intended to conceal what may be considered indecorous or indecent.

It is a borrowing from the French noun cache-sexe, from:
– the verb cacher, translating as to hide;
– the noun sexe, translating as sex, genitals.

The noun cache-sexe occurred, for example, in the column Patrick Marnham’s Paris, by the British author and journalist Patrick Marnham (born 1943), published in the Evening Standard (London, England) of Tuesday 27^th June 1995 [page 27, column 3]:

Sexy search goes on
TODAY the Musée d’Orsay proudly displays its latest acquisition, a Gustave Courbet painting entitled The Origin of the World, a striking nude study focusing on the female sexe until now regarded as too immodest to be shown in public.
The painter never signed the work, which was commissioned by the Turkish ambassador in 1866. He hung his masterpiece in the cabinet de toilette of his Parisian residence and it remained hidden for nearly 130 years. Even the late psychoanalyst Jacques Lacan, whose executors sold the painting to the French Treasury as part of a tax settlement, concealed the offending canvas behind a cache-sexe painted by Andre Masson.

The earliest occurrences that I have found of the noun cache-sexe used in English are as follows, in chronological order:

1-: From In Quest of El Dorado (New York: D. Appleton and Company, 1923), by the British journalist, travel writer, essayist and novelist Stephen Graham (1884-1975) [page 58]:

The wild children of the sun of Haiti will not even bathe in the sea unless discreetly covered. In the Africa whence they came they wore little more than a cache-sexe, but the slaves learned a decorum of dress from the Spaniard in the old Colonial days and it has remained.

2-: From Archaeological News, by Edward H. Heffner, of the University of Pennsylvania, Philadelphia, published in the American Journal of Archaeology: The Journal of the Archaeological Institute of America of January-March 1925 [Vol. XXIX, No. 1, page 102]:

RENNES.—Two Bronze Statuettes.—In R. Arch., fifth series, XIX, 1924, pp. 215-222 (7 figs.), Paul Couissin publishes two bronze statuettes, probably from Egypt, which have been in the archaeological museum at Rennes since 1901. One represents a female dancer or acrobat, who wears only a cache-sexe, bands about the knees, and sandals.

3-: From Some Great English Novels: Studies in the Art of Fiction (London: Macmillan and Co., Limited, 1926), by the British literary critic Orlando Cyprian (‘Orlo’) Williams (1883-1967) [page 158]—the following is from Chapter VI, about Emma (1815), a novel by Jane Austen (1775-1817):

We may imagine, in these days of soul-analysis, of temperaments exposed and of repressions let loose, when it is reputed both brave and fashionable to walk about in psychological nakedness without a cache-sexe of any kind, that we have a great advantage over the repressed and amply breeched and petticoated society of Emma’s day.

4-: From a letter to the Editor, by a person signing themself ‘Argus’, published in The Spectator (London, England) of Saturday 13^th February 1926 [No. 5094, page 270, column 2]:

Sir,—Mr. Angell is wrong in thinking that naked women on the Paris stage are a post-War novelty; I cannot speak of fifteen years ago, but I can speak very definitely of twelve years ago, in 1914, when the two leading music-halls of Paris at least, regularly staged revues the feature of which was two grandes [sic] ensembles of women naked except for the minute cache-sexe. There seemed to be no novelty about these displays.

5-: From In Natura Veritas, by ‘Campanello’, published in The Medical Pickwick. A Monthly Literary Magazine of Wit and Wisdom (St. Louis, Missouri, USA) of September 1926 [Vol. XII, No. 9, page 293, column 2]:

When the shadows grew long, slim figures slipped softly through the streets and went about their business, shy and self-conscious. It was noticeable that they were the fairest of their sex and it was soon seen that they displayed their charms with a growing pride. Shortly they were followed by their less lovely sisters (for it was fast becoming the fashion as well as the law), and their conduct and their carriage became as natural as their costume. One would have thought that it had always been so. The public places resembled the finale of a Paris theatrical revue, but without the least cache-sexe. A hundred thousand nymphs of all ages disported themselves in the warm sun in the costume of Mona Paiva before the Parthenon.

6-: From Custer and Rain In The Face, by the U.S. soldier and author Eli L. Huggins (1842-1929), published in The American Mercury (New York City, New York, USA) of November 1926 [Vol. IX, No. 35, page 343, column 2]:

I heard a few years ago to my surprise that Rain In The Face, before his death, got religion and joined the Church. He discarded the cache sexe and superstitions of the Sioux for the bifurcated garments and superstitions of the pale face.