Eonism [On the name of Chevalier d'Eon (1728-1810), who used to dress in women's clothing]
Eonism is a term derived from Charles Geneviève Louise Auguste André Timothée d'Éon de Beaumont, better known as Chevalier d'Eon (1728-1810). Chevalier d'Éon was a French diplomat, spy, and swordsman who spent much of his adult life dressing as women.
In 1755, d'Eon was sent to Russia on a secret mission, where he introduced himself at the court of Empress Elizabeth Petrovna as Leah de Beaumont. Over the next few decades, d'Eon regularly appeared in public in both female and male guise. His gender duality aroused great interest and speculation among his contemporaries.
In 1777, d'Eon was forced to officially recognize himself as a man in order to return to France. However, he continued to wear women's clothing for the rest of his life. Although d'Eon himself never publicly identified as transgender, his behavior is considered one of the first documented cases of transvestism in history.
Thus, the term "aeonism" is outdated and today is used more in a historical context, referring to a man who cross-dresses in women's clothing. The modern equivalent is transvestism.