E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Cachet (pron. cahshay).
Lettres de cachet (letters sealed). Under the old French régime, carte-blanche warrants, sealed with the kings seal, might be obtained for a consideration, and the
person who held them might fill in any name. Sometimes the warrant was to set a prisoner at large, but it was more frequently for detention in the Bastille. During the administration of Cardinal Fleury 80,000 of these cachets were issued, the larger number being against the Jansenists. In the reigns of Louis XV. and XVI. fifty-nine were obtained against the one family of Mirabeau. This scandal was abolished January 15th, 1790.